Galaxy evolution Research Papers - Academia.edu (original) (raw)

Bar-like structures were investigated in a sample of 186 disk galaxies larger than 0.5 arcsec that are in the I-band image of the Tadpole galaxy taken with the Hubble Space Telescope Advanced Camera for Surveys. We found 22 clear cases of... more

- by
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- Organic Chemistry, Astrophysical Plasma, Star Formation, Galaxy Formation and Evolution

We calculate the projected two point correlation function for samples of luminous and massive galaxies in the COMBO-17 photometric redshift survey, focusing particularly on the amplitude of the correlation function at small projected radii and exploring the constraints such measurements can place on the galaxy merger rate. For nearly volume-limited samples with 0.4 < z < 0.8, we find that 4±1% of luminous M B < −20 galaxies are in close physical pairs (with real space separation of < 30 proper kpc). The corresponding fraction for massive galaxies with M * > 2.5 × 10 10 M ⊙ is 5±1%. Incorporating close pair fractions from the literature, the 2dFGRS and the SDSS, we find a fairly rapid evolution of the merger fraction of massive galaxies between z = 0.8 and the present day. Assuming that the major merger timescale is of order the dynamical timescale for close massive galaxy pairs, we tentatively infer that ∼ 50% (70%) of all galaxies with present-day masses M * > 5 × 10 10 M ⊙ (remnants of mergers between galaxies with M * > 2.5 × 10 10 M ⊙ ) have undergone a major merger since z = 0.8 (1): major mergers between massive galaxies are a significant driver of galaxy evolution over the last eight billion years.

- by S. Phleps
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- Organic Chemistry, Galaxy evolution, Correlation function

The origin of boxy and disky elliptical galaxies is investigated. The results of two collisionless N-body simulations of spiral-spiral mergers with mass ratios of 1:1 and 3:1 are discussed and the projected properties of the merger remnants are investigated. It is shown that the equal-mass merger leads to an anisotropic, slowly rotating system with preferentially boxy isophotes and significant minor axis rotation. The unequal-mass merger results in the formation of a rotationally supported elliptical with disky isophotes and small minor axis rotation. The observed scatter in the kinematical and isophotal properties of both classes of elliptical galaxies can be explained by projection effects.

- by Lars Hernquist
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- Organic Chemistry, Astrophysical Plasma, Galaxy evolution, Elliptical galaxies

Estimates of the interstellar deuterium abundance span a wide range of values. Until recently, it was customary to adopt the abundance of deuterium measured in the Local Bubble as representative of the local one. Now, it is becoming unclear whether the true local deuterium abundance is significantly higher or lower than this value, depending on the interpretation given to current data. It is important to deal with the issue of the deuterium variation and see whether it challenges our current understanding of the Galaxy evolution. To this aim, we study the evolution of deuterium in the framework of successful models for the chemical evolution of the Milky Way able to reproduce the majority of the observational constraints for the solar neighbourhood and for the Galactic disc. We show that, in the framework of our models, the lowest D/H values observed locally cannot be explained in terms of simple astration processes occurring during the Galaxy evolution. Indeed, the combination of a mild star formation and a continuous infall of unprocessed gas required to fit all the available observational data allows only a modest variation of the deuterium abundance from its primordial value. Therefore, we suggest that depletion of deuterium on to dust grains is the most likely physical mechanism proposed so far to explain the observed dispersion in the local data.

- by Francesca Matteucci
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- Star Formation, Chemical Evolution, Galaxy evolution, Milky Way

Gaia is an ambitious space mission of the European Space Agency which will chart a three-dimensional map the Milky Way to study the composition formation and evolution of our Galaxy. Our research team is developing the AVU-GSR verification module, aiming to obtain a reconstruction of the celestial sphere using a subset of GAIA observations. The authors propose a hybrid solution for HPC and Grid-MPI infrastructures which utilizes a modified LSQR -a conjugate gradient-based algorithm -to solve the system of equations for the sphere recostruction. The proposed solution has been selected as pilot test for porting HPC applications in Grid.

- by Alberto Vecchiato
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- Grid Computing, Galaxy evolution, Message Passing, Mathematical Model

Deep extragalactic surveys with ISOCAM revealed the presence of a large density of faint mid-infrared (MIR) sources. We have computed the 15 µm integrated galaxy light produced by these galaxies above a sensitivity limit of 50 µJy. It sets a lower limit to the 15 µm extragalactic background light of (2.4 ± 0.5) nW m −2 sr −1. The redshift distribution of the ISOCAM galaxies is inferred from the spectroscopically complete sample of galaxies in the Hubble Deep Field North (HDFN). It peaks around z ∼ 0.8 in agreement with studies in other fields. The rest-frame 15 µm and bolometric infrared (8-1000 µm) luminosities of ISOCAM galaxies are computed using the correlations that we establish between the 6.75, 12, 15 µm and infrared (IR) luminosities of local galaxies. The resulting IR luminosities were double-checked using radio (1.4 GHz) flux densities from the ultra-deep VLA and WSRT surveys of the HDFN on a sample of 24 galaxies as well as on a sample of 109 local galaxies in common between ISOCAM and the NRAO VLA Sky Survey (NVSS). This comparison shows for the first time that MIR and radio luminosities correlate up to z ∼ 1. This result validates the bolometric IR luminosities derived from MIR luminosities unless both the radio-far infrared (FIR) and the MIR-FIR correlations become invalid around z ∼ 1. The fraction of IR light produced by active nuclei was computed from the cross-correlation with the deepest X-ray surveys from the Chandra and XMM-Newton observatories in the HDFN and Lockman Hole respectively. We find that at most 20% of the 15 µm integrated galaxy light is due to active galactic nuclei (AGNs) unless a large population of AGNs was missed by Chandra and XMM-Newton. About 75% of the ISOCAM galaxies are found to belong to the class of luminous infrared galaxies (LIR ≥ 10 11 L). They exhibit star formation rates of the order of ∼100 M yr −1. The comoving density of infrared light due to these luminous IR galaxies was more than 40 times larger at z ∼ 1 than today. The contribution of ISOCAM galaxies to the peak of the cosmic infrared background (CIRB) at 140 µm was computed from the MIR-FIR correlations for star forming galaxies and from the spectral energy distribution of the Seyfert 2, NGC 1068, for AGNs. We find that the galaxies unveiled by ISOCAM surveys are responsible for the bulk of the CIRB, i.e. (16 ± 5) nW m −2 sr −1 as compared to the (25 ± 7) nW m −2 sr −1 measured with the COBE satellite, with less than 10% due to AGNs. Since the CIRB contains most of the light radiated over the history of star formation in the universe, this means that a large fraction of present-day stars must have formed during a dusty starburst event similar to those revealed by ISOCAM.

We study the evolution of disk galaxies within the frame of the cold dark matter (CDM) cosmologies. The hydrodynamics of a centrifugally supported gaseous disk and the growth of a stellar disk is calculated in detail taking into account the energy balance of the ISM and the gravitational instabilities that concern gas and stars. The halo density profile is derived from the primordial cosmological conditions and its gravitational contraction produced by the disk is included. Several features of the spiral galaxies at different redshifts are predicted, and the main factors which influence on these features are found. A strong evidence is provided that the Tully-Fisher (TF) relation is an imprint of the primordial cosmological conditions.

- by Vladimir Avila-Reese
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- Galaxy evolution, Energy Balance, Spiral Galaxies, Cold Dark Matter

The Galaxy Evolution Explorer (GALEX), a NASA Small Explorer Mission planned for launch in Fall 2002, will perform the first Space Ultraviolet sky survey. Five imaging surveys in each of two bands (1350-1750Å and 1750-2800Å) will range from an all-sky survey (limit m AB~2 0-21) to an ultra-deep survey of 4 square degrees (limit m AB~2 6). Three spectroscopic grism surveys (R=100-300) will be performed with various depths (m AB~2 0-25) and sky coverage (100 to 2 square degrees) over the 1350-2800Å band. The instrument includes a 50 cm modified Ritchey-Chrétien telescope, a dichroic beam splitter and astigmatism corrector, two large sealed tube microchannel plate detectors to simultaneously cover the two bands and the 1.2 degree field of view. A rotating wheel provides either imaging or grism spectroscopy with transmitting optics. We will use the measured UV properties of local galaxies, along with corollary observations, to calibrate the UV-global star formation rate relationship in galaxies. We will apply this calibration to distant galaxies discovered in the deep imaging and spectroscopic surveys to map the history of star formation in the universe over the red shift range zero to two. The GALEX mission will include an Associate Investigator program for additional observations and supporting data analysis. This will support a wide variety of investigations made possible by the first UV sky survey.

- by Amit Sen
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- Data Analysis, Star Formation, Proceedings, Ultraviolet

We model the abundance gradients in the disk of the Milky Way for several chemical elements (O, Mg, Si, S, Ca, Sc, Ti, Co, V, Fe, Ni, Zn, Cu, Mn, Cr, Ba, La and Eu), and compare our results with the most recent and homogeneous observational data. We adopt a chemical evolution model able to well reproduce the main properties of the solar vicinity. We compute, for the first time, the abundance gradients for all the above mentioned elements in the galactocentric distance range 4 - 22 kpc. The comparison with the observed data on Cepheids in the galactocentric distance range 5-17 kpc gives a very good agreement for many of the studied elements. In addition, we fit very well the data for the evolution of Lanthanum in the solar vicinity for which we present results here for the first time. We explore, also for the first time, the behaviour of the abundance gradients at large galactocentric distances by comparing our results with data relative to distant open clusters and red giants and select the best chemical evolution model model on the basis of that. We find a very good fit to the observed abundance gradients, as traced by Cepheids, for most of the elements, thus confirming the validity of the inside-out scenario for the formation of the Milky Way disk as well as the adopted nucleosynthesis prescriptions.

Using simulations of box/peanut-(B/P-) shaped bulges, we explore the nature of the X-shape of the Milky Way's bulge. An X-shape can be associated with a B/Pshaped bulge driven by a bar. By comparing in detail the simulations and the observations we show that the principal kinematic imprint of the X-shape is a minimum in the difference between the near and far side mean line-of-sight velocity along the minor axis. This minimum occurs at around |b| = 4 • , which is close to the lower limit at which the X-shape can be detected. No coherent signature of an X-shape can be found in Galactocentric azimuthal velocities, vertical velocities, or any of the dispersions. After scaling our simulations, we find that a best fit to the Bulge Radial Velocity Assay data leads to a bar angle of 15 •. We also explore a purely geometric method for determining the distance to the Galactic Centre by tracing the arms of the X-shape. We find that we are able to determine this ill-known distance to an accuracy of about 5% with sufficiently accurate distance measurements for the red clump stars in the arms.

- by Sarita Vasquez
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- Physics, Astrophysics, Galaxy evolution, Galaxy

We present the first determination of the radial velocities and metallicities of 78 red giant stars in the isolated dwarf irregular galaxy WLM. Observations of the calcium II triplet in these stars were made with FORS2 at the VLT-UT2 in two separated fields of view in WLM, and the [Fe/H] values were conformed to the Carretta & Gratton ([Fe/H] CG97 ) metallicity scale. The mean metallicity is [Fe/H] = −1.27 ± 0.04 dex, with a standard deviation of σ = 0.37. We find that the stars in the inner field are more metal-rich by Δ[Fe/H]= 0.30 ± 0.06 dex. These results are in agreement with previous photometric studies that found a radial population gradient, as well as the expectation of higher metallicities in the central star-forming regions. Age estimates using Victoria-Regina stellar models show that the youngest stars in the sample (less than 6 Gyr) are more metal-rich by Δ[Fe/H]= 0.32 ± 0.08 dex. These stars also show a lower velocity dispersion at all elliptical radii compared to the metal-poor stars. Kinematics for the whole red giant sample suggest a velocity gradient approximately half that of the gas rotation curve, with the stellar component occupying a thicker disk decoupled from the H i rotation plane. Taken together, the kinematics, metallicities, and ages in our sample suggest a young metal-rich, and kinematically cold stellar population in the central gas-rich regions of WLM, surrounded by a separate dynamically hot halo of older, metal-poor stars.

Possibility of Perpetual Source of Energy

- by Ramkrishna Das
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- Evolutionary Biology, Cognitive Science, Mathematics, Number Theory

We describe the Galaxy Evolution Explorer (GALEX) satellite that was launched in April 2003 specifically to accomplish far ultraviolet (FUV) and near ultraviolet (NUV) imaging and spectroscopic sky-surveys. GALEX is currently providing... more

- by roger malina
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- Star Formation, Galactic Astronomy, Proceedings, Sensors

In this work we investigate the stellar content of three circumnuclear giant H II regions in the starburst galaxy NGC 7714. We model the stellar population that best reproduces the observational constraints given by the Ha image and the... more

- by Ángeles Díaz
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- Organic Chemistry, Astrophysical Plasma, Star Formation, Optical Spectroscopy

The current standard model of cosmology (SMoC) requires The Dual Dwarf Galaxy Theorem to be true according to which two types of dwarf galaxies must exist: primordial dark-matter (DM) dominated (type A) dwarf galaxies, and tidal-dwarf and ram-pressure-dwarf (type B) galaxies void of DM. Type A dwarfs surround the host approximately spherically, while type B dwarfs are typically correlated in phasespace. Type B dwarfs must exist in any cosmological theory in which galaxies interact. Only one type of dwarf galaxy is observed to exist on the baryonic Tully-Fisher plot and in the radius-mass plane. The Milky Way satellite system forms a vast phase-space-correlated structure that includes globular clusters and stellar and gaseous streams. Other galaxies also have phase-space correlated satellite systems. Therefore, The Dual Dwarf Galaxy Theorem is falsified by observation and dynamically relevant cold or warm DM cannot exist. It is shown that the SMoC is incompatible with a large set of other extragalactic observations. Other theoretical solutions to cosmological observations exist. In particular, alone the empirical mass-discrepancyacceleration correlation constitutes convincing evidence that galactic-scale dynamics must be Milgromian. Major problems with inflationary big bang cosmologies remain unresolved.

- by Pavel Kroupa
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- Gravitation, Dark Matter, Theory, Modeling

We consider the Universe deep inside the cell of uniformity. At these scales, the Universe is filled with inhomogeneously distributed discrete structures (galaxies, groups and clusters of galaxies), which perturb the background Friedmann model. Here, the mechanical approach (Eingorn & Zhuk, 2012) is the most appropriate to describe the dynamics of the inhomogeneities which is defined, on the one hand, by gravitational potentials of inhomogeneities and, on the other hand, by the cosmological expansion of the Universe. In this paper, we present additional arguments in favor of this approach. First, we estimate the size of the cell of uniformity. With the help of the standard methods of statistical physics and for the galaxies of the type of the Milky Way and Andromeda, we get that it is of the order of 190 Mpc which is rather close to observations. Then, we show that the nonrelativistic approximation (with respect to the peculiar velocities) is valid for zlesssim10z \lesssim 10zlesssim10, i.e. approximately for 13 billion years from the present moment. We consider scalar perturbations and, within the Lambda\LambdaLambdaCDM model, justify the main equations. Moreover, we demonstrate that radiation can be naturally incorporated into our scheme. This emphasizes the viability of our approach. This approach gives a possibility to analyze different cosmological models and compare them with the observable Universe. For example, we indicate some problematic aspects of the spatially flat models. Such models require a rather specific distribution of the inhomogeneities to get a finite potential at any points outside gravitating masses. We also criticize the application of the Schwarzschild-de Sitter solution to the description of the motion of test bodies on the cosmological background.

- by Maxim Eingorn
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- Mathematical Physics, Geometry And Topology, Physics, Theoretical Physics

We set out to determine the ratio, q(IR), of rest-frame 8-1000um flux, S(IR), to monochromatic radio flux, S(1.4GHz), for galaxies selected at far-IR and radio wavelengths, to search for signs that the ratio evolves with redshift, luminosity or dust temperature, and to identify any far-IR-bright outliers - useful laboratories for exploring why the far-IR/radio correlation is generally so tight when the prevailing theory suggests variations are almost inevitable. We use flux-limited 250-um and 1.4-GHz samples, obtained in GOODS-N using Herschel (HerMES; PEP) and the VLA. We determine bolometric IR output using ten bands spanning 24-1250um, exploiting data from PACS and SPIRE, as well as Spitzer, SCUBA, AzTEC and MAMBO. We also explore the properties of an L(IR)-matched sample, designed to reveal evolution of q(IR) with z, spanning log L(IR) = 11-12 L(sun) and z=0-2, by stacking into the radio and far-IR images. For 1.4-GHz-selected galaxies, we see tentative evidence of a break in the flux ratio, q(IR), at L(1.4GHz) ~ 10^22.7 W/Hz, where AGN are starting to dominate the radio power density, and of weaker correlations with z and T(d). From our 250-um-selected sample we identify a small number of far-IR-bright outliers, and see trends of q(IR) with L(1.4GHz), L(IR), T(d) and z, noting that some of these are inter-related. For our L(IR)-matched sample, there is no evidence that q(IR) changes significantly as we move back into the epoch of galaxy formation: we find q(IR) goes as (1+z)^gamma, where gamma = -0.04 +/- 0.03 at z=0-2; however, discounting the least reliable data at z<0.5 we find gamma = -0.26 +/- 0.07, modest evolution which may be related to the radio background seen by ARCADE2, perhaps driven by <10uJy radio activity amongst ordinary star-forming galaxies at z>1.

We have used the Hubble Space Telescope's Advanced Camera for Surveys to measure the mass density function of morphologically-selected early-type galaxies in the Gemini Deep Deep Survey fields, over the redshift range 0.9 < z < 1.6. Our imaging data set covers four well-separated sight-lines, and is roughly intermediate (in terms of both depth and area) between the GOODS/GEMS imaging data, and the images obtained in the Hubble Deep Field campaigns. Our images contain 144 galaxies with ultra-deep spectroscopy, and they have been analyzed using a new purpose-written morphological analysis code which improves the reliability of morphological classifications by adopting a 'quasi-petrosian' image thresholding technique. We find that at z = 1 approximately 70% of the stars in massive galaxies reside in early-type systems. This fraction is remarkably similar to that seen in the local Universe. However, we detect very rapid evolution in this fraction over the range 1.0 < z < 1.6, suggesting that in this epoch the strong color-morphology relationship seen in the nearby Universe is beginning to fall into place.

- by Roberto Abraham and +1
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- Morphology, Galaxy Formation and Evolution, Density-functional theory, Density Functional Theory

First epoch VVDS-Deep survey: 11564 spectra with 17.5 ≤ I AB ≤ 24, and the redshift distribution over 0 ≤ z ≤ 5

- by P. Taxil and +1
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- Star Formation, Dark Matter, Galaxy Formation and Evolution, Galaxy Clusters

We explore galaxy properties in general and properties of host galaxies of gammaray bursts (GRBs) in particular, using N-body/Eulerian hydrodynamic simulations and the stellar population synthesis model, Starburst99, to infer observable properties. We identify simulated galaxies that have optical star formation rate (SFR) and SFRto-luminosity ratio similar to those observed in a well-defined sample of ten host galaxies. Each of the numerical counterparts are found in catalogs at the same redshifts as the observed hosts. The counterparts are found to be low-mass galaxies, with low mass-to-light ratio, recent epoch of formation, and high ratio between the SFR and the average of the SFR. When compared to the overall galaxy population, they have colors much bluer than the high-mass star-forming galaxy population. Although their SFRs span a range of values, the specific rates of the numerical counterparts are equal to or higher than the median values estimated at the different redshifts. We also emphasize the strong relationships between the specific star formation rate (SFR) and quantities known to reflect the star formation history of galaxies, i.e. color and mass-to-light ratio: At intermediate redshift, the faintest and bluest galaxies are also the objects with the highest specific rates. These results suggest that GRB host galaxies are likely to be drawn from the high specific SFR sub-population of galaxies, rather than the high SFR galaxy population. Finally, as indicated by our catalogs, in an extended sample, the majority of GRB host galaxies is expected to have specific SFRs higher than found in the magnitude-limited sample studied here.

- by Einar Gudmundsson
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- Star Formation, Galaxy Formation and Evolution, Color, Galaxy evolution

We present near-infrared spectroscopy and Hubble Space Telescope (HST) imaging of ERO J003707+0909.5, the brightest of three gravitationally-lensed images of an Extremely Red Object (ERO) at z = 1.6, in the field of the massive cluster A 68 (z = 0.255). We exploit the superlative resolution of our HST data and the enhanced spatial resolution and sensitivity afforded by the lens amplification to reconstruct the source-plane properties of this ERO. Our morphological and photometric analysis reveals that ERO J003707 is an L ⋆ early-type disk-galaxy and we estimate that ∼ 10 per cent of EROs with (R − K) ≥ 5.3 and K ≤ 21 may have similar properties. The unique association of passive EROs with elliptical galaxies therefore appears to be too simplistic. We speculate on the evolution of ERO J003707: if gas continues to cool onto this galaxy in the manner predicted by hierarchical galaxy formation models, then by the present day, ERO J003707 could evolve into a very luminous spiral galaxy.

- by Harald Ebeling
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- Thermodynamics, Organic Chemistry, Astrophysical Plasma, Dark Matter

We develop a new method to constrain the star formation histories, dust attenuation and stellar masses of galaxies. It is based on two stellar absorption line indices, the 4000Å break strength and the Balmer absorption line index Hδ A . Together, these indices allow us to constrain the mean stellar ages of galaxies and the fractional stellar mass formed in bursts over the past few Gyr. A comparison with broad band photometry then yields estimates of dust attenuation and of stellar mass. We generate a large library of Monte Carlo realizations of different star formation histories, including starbursts of varying strength and a range of metallicities. We use this library to generate median likelihood estimates of burst mass fractions, dust attenuation strengths, stellar masses and stellar mass-to-light ratios for a sample of 122,808 galaxies drawn from the Sloan Digital Sky Survey. The typical 95% confidence range in our estimated stellar masses is ± 40 %. We study how the stellar mass-to-light ratios of galaxies vary as a function of absolute magnitude, concentration index and photometric pass-band and how dust attenuation varies as a function of absolute magnitude and 4000Å break strength. We also calculate how the total stellar mass of the present Universe is distributed over galaxies as a function of their mass, size, concentration, colour, burst mass fraction and surface mass density. We find that most of the stellar mass in the local Universe resides in galaxies that have, to within a factor of about 2, stellar masses ∼ 5×10 10 M ⊙ , half-light radii ∼ 3 kpc, and half-light surface mass densities ∼ 10 9 M ⊙ kpc −2 . The distribution of D n (4000) is strongly bimodal, showing a clear division between galaxies dominated by old stellar populations and galaxies with more recent star formation.

- by Jarle Brinchmann
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- Star Formation, Monte Carlo, Galaxy Formation and Evolution, Galaxy evolution

The weak radio source LBDS 53W091 is associated with a very faint (R approx. 24.5) red (R-K approx. 5.8) galaxy. Long spectroscopic integrations with the W. M. Keck telescope have provided an absorption-line redshift, z=1.552 +/- 0.002. The galaxy has a rest frame ultraviolet spectrum very similar to that of an F6V star, and a single-burst old stellar population that matches the IR colors, the optical energy distribution and the spectral discontinuities has a minimum age of 3.5 Gyr. We present detailed population synthesis analyses of the observed spectrum in order to estimate the time since the last major epoch of star formation. We discuss the discrepancies in these estimates resulting from using different models, subjecting the UV spectrum of M32 to the same tests as a measure of robustness of these techniques. The models most consistent with the data tend to yield ages at z=1.55 of >3.5Gyr, similar to that inferred for the intermediate-age population in M32. Depending upon the assumed Hubble constant and the value of Omega_0, only certain cosmological expansion times are consistent with the age of LBDS 53W091; in particular, for Omega_0=1, only models with H_0 < 45 km/s/Mpc are permitted. For H_0=50 km/s/Mpc and Omega_0=0.2, we derive a formation redshift, z_f >= 5.

- by Arjun Dey
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- Organic Chemistry, Astrophysical Plasma, Star Formation, Ultraviolet

(Abbrev.) This paper prepares a series of papers analysing the Intermediate MAss Galaxy Evolution Sequence (IMAGES) up to z=1. Intermediate mass galaxies (MJ <=-20.3) are selected from the Chandra Deep Field South (CDFS) for which we identify a serious lack of spectroscopically determined redshifts..... We have spectroscopically identified 691 objects including 580 gal., 7 QSOs, and 104 stars. This study provides 531 new redshifts in the CDFS. It confirms the presence of several large scale structures in the CDFS. To test the impact of these structures in the GOODS-South field, we ... compare the evolution of rest-frame U, B, V and K galaxy luminosity densities to that derived from the CFRS. The CDFS field shows a significant excess of luminosity densities in the z=0.5-0.75 range, which increases with the wavelength, reaching up to 0.5 dex at 2.1 um. Stellar mass and specific star formation evolutions might be significantly affected by the presence of the peculiar large scale structures at z= 0.668 and at z= 0.735, that contain a significant excess of evolved, massive galaxies when compared to other fields. This leads to a clear warning to results based on the CDFS/GOODS South fields, especially those related to the evolution of red luminosity densities, i.e. stellar mass density and specific star formation rate. Photometric redshift techniques, when applied to that field, are producing quantities which are apparently less affected by cosmic variance (0.25 dex at 2.1 um), however at the cost of the difficulty in disentangling between evolutionary and cosmic variance effects.

We report the discovery of an almost complete Einstein ring of diameter 10" in Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5). Spectroscopic data from the 6m telescope of the Special Astrophysical Observatory reveals that the deflecting galaxy has a line-of-sight velocity dispersion in excess of 400 km/s and a redshift of 0.444, whilst the source is a star-forming galaxy with a redshift of 2.379. From its color and luminosity, we conclude that the lens is an exceptionally massive Luminous Red Galaxy (LRG) with a mass within the Einstein radius of 5 x 10^12 solar masses. This remarkable system provides a laboratory for probing the dark matter distribution in LRGs at distances out to 3 effective radii, and studying the properties of high redshift star-forming galaxies.

We have performed an X-ray study of the nearby barred spiral galaxy NGC 1672, primarily to ascertain the effect of the bar on its nuclear activity. We use both Chandra and XMM-Newton observations to investigate its X-ray properties, together with supporting high-resolution optical imaging data from the Hubble Space Telescope (HST), infrared imaging from the Spitzer Space Telescope, and ATCA ground-based radio data. We detect 28 X-ray sources within the D 25 area of the galaxy, many of which correlate spatially with starformation in the bar and spiral arms, while two are identified as background galaxies in the HST images. Nine of the X-ray sources are ULXs, with the three brightest (L X > 5 × 10 39 erg s −1 ) located at the ends of the bar. With the spatial resolution of Chandra, we are able to show for the first time that NGC 1672 possesses a hard (Γ ∼ 1.5) nuclear X-ray source with a 2-10 keV luminosity of 4 × 10 38 erg s −1 . This is surrounded by an X-ray bright circumnuclear star-forming ring, comprised of point sources and hot gas, which dominates the 2-10 keV emission in the central region of the galaxy. The spatially resolved multiwavelength photometry indicates that the nuclear source is a low-luminosity AGN (LLAGN), but with star formation activity close to the central black hole. A high-resolution multiwavelength survey is required to fully assess the impact of both large-scale bars and smaller-scale phenomena such as nuclear bars, rings and nuclear spirals on the fueling of LLAGN.

- by B. Koribalski
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- Organic Chemistry, Astrophysical Plasma, Star Formation, Optical Imaging

We discuss the importance of very metal-poor stars to develop an understanding of the nature of the first stars that formed in the Universe and the nucleosynthesis events associated with them, as well as to refine models of galaxy formation, in particular for large spiral galaxies such as the Milky Way. After briefly reviewing the history of the search for

- by Timothy Beers
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- Carbon, Evolution, Galaxy Formation and Evolution, Dust (Astronomy & Astrophysics)

We present an application of the da Cunha, model of the spectral energy distribution (SEDs) of galaxies from the ultraviolet to far-infrared, to a small pilot sample of purely star-forming Ultra-Luminous Infrared Galaxies (ULIRGs). We interpret the observed SEDs of 16 ULIRGs using this physically-motivated model which accounts for the emission of stellar populations from the ultraviolet to the near-infrared and for the attenuation by dust in two components: an optically-thick starburst component and the diffuse ISM. The infrared emission is computed by assuming that all the energy absorbed by dust in these components is re-radiated at mid-and far-infrared wavelengths. This model allows us to derive statistically physical properties including star formation rates, stellar masses, as well as temperatures and masses of different dust components and plausible star formation histories. We find that, although the ultraviolet to near-infrared emission represents only a small fraction of the total power radiated by ULIRGs, observations in this wavelength range are important to understand the properties of the stellar populations and dust attenuation in the diffuse ISM of these galaxies. Furthermore, our analysis indicates that the use of mid-infrared spectroscopy from the Infrared Spectrograph on the Spitzer Space Telescope is crucial to obtain realistic estimates of the extinction to the central energy source, mainly via the depth of the 9.7-µm silicate feature, and thus accurately constrain the total energy balance. Our findings are consistent with the notion that, in the local Universe, the physical properties of ULIRGs are fundamentally different from those of galaxies with lower infrared luminosities and that local ULIRGs are the result of merger-induced starbursts. While these are well-established ideas, we demonstrate the usefulness of our SED modelling in deriving relevant physical parameters which provide clues to the star formation mode of galaxies.

This paper is nothing short of a positive and complete verification of the unification of current physics paradigms of single field theory (SOFT) in light of recently published observational data in astronomy. An article by Sabine Hossenfelder and Stacey S. McGaugh, titled " Is Dark Matter Real?', has just appeared in the August 2018 issue of Scientific American. Every physicist, astronomer, astrophysicist and cosmologist as well as everyone interested in science needs to read this article because it portends one of the greatest scientific advances in several hundred years, the complete unification of physics and science in general. Due to new observational evidence in astronomy, they have concluded that " Astrophysicists have piled up observations that are difficult to explain with Dark Matter. It is time to consider that there may be more to gravity than Einstein taught us. " But they have understated the case. In effect, the new observational data found by McGaugh and an international group of astronomers clearly shows that specifically designated dark matter particles do not exist, so the supposed Dark Matter halos around spiral galaxies do not exist and the rotational speed discrepancies in galaxy orbiting stars and star systems that go unaccounted for by normal gravity are, in fact, due to a secondary effect of normal matter within the galaxy. This finding not only challenges the present theories of gravity (Newtonian and Einsteinian), which it demonstrates are incomplete, it also blows some big logical holes in the fundamentality of the quantum theory, the Standard Model of point-particles and quantum field theories in general that seem to rule the world of modern theoretical physics. Given other recent confirmations of Einstein's general relativity, found mostly in the detection of gravitational waves that Einstein predicted a century ago, relativity theory seems on the ascendancy and quantum theory is falling behind. The time for a unified field theory that combines the best of both paradigms is at hand.

We present an updated, optimized version of GAME (GAlaxy Machine learning for Emission lines), a code designed to infer key interstellar medium physical properties from emission line intensities of UV/optical/far infrared galaxy spectra. The improvements concern: (a) an enlarged spectral library including Pop III stars; (b) the inclusion of spectral noise in the training procedure, and (c) an accurate evaluation of uncertainties. We extensively validate the optimized code and compare its performance against empirical methods and other available emission line codes (PYQZ and HII-CHI-MISTRY) on a sample of 62 SDSS stacked galaxy spectra and 75 observed HII regions. Very good agreement is found for metallicity. However, ionization parameters derived by GAME tend to be higher. We show that this is due to the use of too limited libraries in the other codes. The main advantages of GAME are the simultaneous use of all the measured spectral lines, and the extremely short computational times. We finally discuss the code potential and limitations.

- by Graziano UCCI and +1
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- Interstellar Medium, Machine Learning, Galaxy Formation and Evolution, High Redshift Universe

We present first results from Galaxy Zoo 2, the second phase of the highly successful Galaxy Zoo project (www.galaxyzoo.org). Using a volume-limited sample of 13665 disk galaxies (0.01 < z < 0.06 and M r < −19.38), we study the fraction of galaxies with bars as a function of global galaxy properties like colour, luminosity and bulge prominence. Overall, 29.4 ± 0.5% of galaxies in our sample have a bar, in excellent agreement with previous visually-classified samples of galaxies (although this overall fraction is lower than measured by automated bar-finding methods). We see a clear increase in the bar fraction with redder (g − r) colours, decreased luminosity and in galaxies with more prominent bulges, to the extent that over half of the red, bulge-dominated, disk galaxies in our sample possess a bar. We see evidence for a colour bi-modality for our sample of disk galaxies, with a "red sequence" that is both bulge and bar-dominated, and a "blue cloud" which has little, or no, evidence for a (classical) bulge or bar. These results are consistent with similar trends for barred galaxies seen recently both locally and at higher redshift, and with early studies using the RC3. We discuss these results in the context of internal (secular) galaxy evolution scenarios and the possible links to the formation of bars and bulges in disk galaxies.

- by Steven Bamford
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- Galaxy Formation and Evolution, Galaxy evolution, Spiral Galaxies

We use data from the Herschel-ATLAS to investigate the evolution of the far-infraredradio correlation over the redshift range 0 < z < 0.5. Using the total far-infrared luminosity of all > 5σ sources in the Herschel-ATLAS Science Demonstration Field and cross-matching these data with radio data from the Faint Images of the Radio Sky at Twenty-Centimetres (FIRST) survey and the NRAO VLA Northern Sky Survey (NVSS), we obtain 104 radio counterparts to the Herschel sources. With these data we find no evidence for evolution in the far-infrared-radio correlation over the redshift range 0 < z < 0.5, where the median value for the ratio between far-infrared and radio luminosity, q IR , over this range is q IR = 2.40 ± 0.12 (and a mean of q IR = 2.52 ± 0.03 accounting for the lower limits), consistent with both the local value determined from IRAS and values derived from surveys targeting the high-redshift Universe. By comparing the radio fluxes of our sample measured from both FIRST and NVSS we show that previous results suggesting an increase in the value of q IR from high to low redshift may be the result of resolving out extended emission of the low-redshift sources with relatively high-resolution interferometric data, although AGN contamination could still play a significant role.

- by Aaron Robotham
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- Active Galactic Nuclei, High Redshift Universe, Galaxy evolution, High Resolution

The Spitzer SDSS GALEX Spectroscopic Survey (SSGSS) provides a new sample of 101 star-forming galaxies at z < 0.2 with unprecedented multi-wavelength coverage. New mid-to far-infrared spectroscopy from the Spitzer Space Telescope is added to a rich suite of previous imaging and spectroscopy, including ROSAT, GALEX, SDSS, 2MASS, and Spitzer/SWIRE. Sample selection ensures an even coverage of the full range of normal galaxy properties, spanning two orders of magnitude in stellar mass, colour, and dust attenuation. In this paper we present the SSGSS data set, describe the science drivers, and detail the sample selection, observations, data reduction, and quality assessment. Also in this paper, we compare the shape of the thermal continuum and the degree of silicate absorption of these typical, star-forming galaxies to those of starburst galaxies. We investigate the link between star formation rate, infrared luminosity, and total PAH luminosity, with a view to calibrating the latter for SED models in photometric samples and at high redshift. Lastly, we take advantage of the 5-40 µm spectroscopic and far infrared photometric coverage of this sample to perform detailed fitting of the Draine et al. dust models, and investigate the link between dust mass and star formation history and AGN properties.

We study the Kennicutt-Schmidt star formation law and efficiency in the gaseous disk of the isolated galaxy CIG 96 (NGC 864), with special emphasis on its unusually large atomic gas (H i) disk (r H i /r 25 = 3.5, r 25 = 1. 85). We present deep Galaxy Evolution Explorer near-and far-UV observations, used as a recent star formation tracer, and we compare them with new, high-resolution (16 or 1.6 kpc) Very Large Array H i observations. The UV and H i maps show good spatial correlation outside the inner 1 , where the H i phase dominates over H 2 . Star-forming regions in the extended gaseous disk are mainly located along the enhanced H i emission within two (relatively) symmetric, giant gaseous spiral arm-like features, which emulate an H i pseudo-ring at r 3 . Inside this structure, two smaller gaseous spiral arms extend from the northeast and southwest of the optical disk and connect to the previously mentioned H i pseudo-ring. Interestingly, we find that the (atomic) Kennicutt-Schmidt power-law index systematically decreases with radius, from N 3.0 ± 0.3 in the inner disk (0. 8-1. 7) to N = 1.6 ± 0.5 in the outskirts of the gaseous disk (3. 3-4. 2). Although the star formation efficiency (SFE), the star formation rate per unit of gas, decreases with radius where the H i component dominates as is common in galaxies, we find that there is a break of the correlation at r = 1.5r 25 . At radii 1.5r 25 < r < 3.5r 25 , mostly within the H i pseudo-ring structure, regions exist whose SFE remains nearly constant, SFE 10 −11 yr −1 . We discuss possible mechanisms that might be triggering the star formation in the outskirts of this galaxy, and we suggest that the constant SFE for such large radii (r > 2r 25 ) and at such low surface densities might be a common characteristic in extended UV disk galaxies.

- by José Sabater Montes
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- Organic Chemistry, Astrophysical Plasma, Star Formation, Galaxy evolution

Over the past years observations of young and populous star clusters have shown that the stellar IMF appears to be an invariant featureless Salpeter power-law with an exponent α = 2.35 for stars more massive than a few M ⊙ . A consensus has also emerged that most, if not all, stars form in stellar groups and star clusters, and that the mass function of young star clusters in the solar-neighborhood and in interacting galaxies can be described, over the mass range of a few 10 M ⊙ to 10 7 M ⊙ , as a power-law with an exponent β ≈ 2. These two results imply that galactic-field IMFs for early-type stars cannot, under any circumstances, be a Salpeter power-law, but that they must have a steeper exponent α field > ∼ 2.8. This has important consequences for the distribution of stellar remnants and for the chemo-dynamical and photometric evolution of galaxies.

- by Pavel Kroupa
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- Organic Chemistry, Astrophysical Plasma, Galaxy evolution, Power Law

Analyses of high-redshift ultraluminous infrared (IR) galaxies traditionally use the observed optical to submillimeter spectral energy distribution (SED) and estimates of the dynamical mass as observational constraints to derive the star formation rate (SFR), the stellar mass, and age of these objects. An important observational constraint neglected in the analysis is the mass of dust giving rise to the IR emission. In this paper we add this constraint to the analysis of AzTEC-3. Adopting an upper limit to the mass of stars and a bolometric luminosity for this object, we construct different stellar and chemical evolutionary scenarios, constrained to produce the inferred dust mass and observed luminosity before the associated stellar mass exceeds the observational limit. We use the PÉGASE population synthesis code and a chemical evolution model to follow the evolution of the galaxy's SED and its stellar and dust masses as a function of galactic age for seven different stellar initial mass functions (IMFs). We find that the model with a Top Heavy IMF provided the most plausible scenario consistent with the observational constraints. In this scenario the dust formed over a period of ~200 Myr, with an SFR of ~500 M sun yr-1. These values for the age and SFR in AzTEC-3 are significantly higher and lower, respectively, from those derived without the dust mass constraint. However, this scenario is not unique, and others cannot be completely ruled out because of the prevailing uncertainties in the age of the galaxy, its bolometric luminosity, and its stellar and dust masses. A robust result of our models is that all scenarios require most of the radiating dust mass to have been accreted in molecular clouds. Our new procedure highlights the importance of a multiwavelength approach, and of the use of dust evolution models in constraining the age and the star formation activity and history in galaxies.

- by Elmer Elí
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- Organic Chemistry, Astrophysical Plasma, Star Formation, Chemical Evolution

We outline a simple approach to understanding the physical origin of bias in the distribution of galaxies relative to that of dark matter. The rst step is to specify how collapsed, virialized halos of dark matter trace the overall matter... more

- by Matthias Steinmetz
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- Dark Matter, Galaxy Formation and Evolution, Galaxy evolution, High Resolution
- by Matthew Lehnert
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- Earth Sciences, Astronomy, Galaxy evolution, Physical sciences

We investigate the production of nitrogen in star forming galaxies with ultraviolet (UV) radiation detected by the Galaxy Evolution Explorer Satellite (GALEX). We use a sample of 8,745 GALEX emission line galaxies matched to the Sloan Digital Sky Survey (SDSS) spectroscopic sample. We derive both gas-phase oxygen and nitrogen abundances for the sample, and apply stellar population synthesis models to derive stellar masses and star formation histories of the galaxies. We compare oxygen abundances derived using three different diagnostics. We derive the specific star formation rates of the galaxies by modeling the 7−band GALEX+SDSS photometry. We find that galaxies that have log SFR/M * −10.0 typically have values of log N/O ∼ 0.05 dex less than galaxies with log SFR/M * −10.0 and similar oxygen abundances.

- by Barry Welsh
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- Organic Chemistry, Ultraviolet, Galaxy evolution, Uv Radiation

One of the central issues in astronomy is the formation and evolution of galaxies at large redshifts. Submillimeter observations are essential to understanding these processes. One of the best prospects for high redshift submillimeter observations is the study of the Cii 158 m ne-structure line, which carries about 0.2% of the total luminosity of nearby starburst galaxies. However, current heterodyne receivers at submillimeter observatories have insu cient bandwidth to detect the full extent of highly broadened emission lines. We are developing a broadband grating spectrometer for the Caltech Submillimeter Observatory with a total bandwidth of 3400 km/s and a velocity resolution of 200 km/s. The detectors will be a linear array of 32 close-packed monolithic silicon bolometers developed at NASA's Goddard Space Flight Center. In order to achieve background-limited sensitivity, the bolometers will be cooled to 100mK by an adiabatic demagnetization refrigerator. The spectrometer optics will consist of a tunable cryogenic immersion grating using broadband lters as order sorters. The spectrometer will be optimized to operate in the 350 m and 450 m atmospheric windows. Calculations of the sensitivity of the spectrometer reveal that an ultraluminous infrared galaxy of 10 12 L at a redshift of z = 1 would be detectable at the 3 level in the Cii line with 20 minutes of integration time.

- by Dominic Benford
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- Optics, Galactic Astronomy, Astronomy, Sensors

We present an analysis of the spatial orientations of 1315 galaxies in 10 Abell clusters of BM type II-III (type II-III in the Bautz-Morgan system). It is found that the spin-vector orientations of the galaxies in six clusters (Abell 168, 426, 1035(Abell 168, 426, , 1227(Abell 168, 426, , 1367(Abell 168, 426, and 1904 tend to lie parallel to the Local Supercluster (LSC) plane. The spin-vector projections of galaxies in six clusters (Abell 168, 1020(Abell 168, , 1035(Abell 168, , 1227(Abell 168, , 1904(Abell 168, and 1920 are found to be oriented perpendicular with respect to the direction of the LSC centre. Three clusters (Abell 1920(Abell , 2255(Abell and 2256 show a bimodal orientation: spin vectors tend to be oriented both parallel and perpendicular to the LSC plane. No dependence of radial velocity, distance and cluster magnitude on galaxy orientation is noticed. In a comparison with previous work, we noticed that the anisotropy might increase from early-type (BM type I) to late-type (BM types II-III and III) clusters. We notice a vanishing angular momentum for the less massive galaxy clusters (richness class 0). A significant alignment of the angular momenta of galaxies for massive clusters, e.g. the core of the Shapley Supercluster (richness class 4, M > 10 15 M ), is found.

- by B. Aryal
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- Galaxy Formation and Evolution, Galaxy Clusters, Galaxy evolution, Radial Velocity

We analyze the observed properties of nested and single stellar bar systems in disk galaxies. The 112 galaxies in our sample comprise the largest matched Seyfert vs. non-Seyfert galaxy sample of nearby galaxies with complete near-infrared or optical imaging sensitive to lengthscales ranging from tens of pc to tens of kpc. The presence of bars is deduced by fitting ellipses to isophotes in HST H-band images up to 10 ′′ radius, and in ground-based near-infrared and optical images outside the H-band images. This is a conservative approach that is likely to result in an underestimate of the true bar fraction. We find that a significant fraction of the sample galaxies, 17% ± 4%, has more than one bar, and that 28% ± 5% of barred galaxies have nested bars. The bar fractions appear to be stable according to reasonable changes in our adopted bar criteria. For the nested bars, we detect a clear division in length between the large-scale (primary) bars and small-scale (secondary) bars, both in absolute and normalized (to the size of the galaxy) length. We argue that this bimodal distribution can be understood within the framework of disk resonances, specifically the inner Lindblad resonances (ILRs), which are located where the gravitational potential of the innermost galaxy switches effectively from 3D to 2D. This conclusion is further strengthened by the observed distribution of the sizes of nuclear rings which are dynamically associated with the ILRs. While primary bars are found to correlate with the host galaxy sizes, no such correlation is observed for the secondary bars. Moreover, we find that secondary bars differ morphologically from single bars. Our matched Seyfert and non-Seyfert samples show a statistically significant excess of bars among the Seyfert galaxies at practically all lengthscales. We confirm our previous results that bars are more abundant in Seyfert hosts than in non-Seyferts, and that Seyfert galaxies always show a preponderance of "thick" bars compared to the bars in non-Seyfert galaxies. Finally, no correlation is observed between the presence of a bar and that of companion galaxies, even relatively bright ones. Overall, since star formation and dust extinction can be significant even in the H-band, the stellar dynamics of the central kiloparsec cannot always be revealed reliably by the use of near-infrared surface photometry alone.

- by I. Shlosman
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- Organic Chemistry, Astrophysical Plasma, Near Infrared, Optical Imaging

One of the key goals of NASA's astrophysics program is to answer the question: How did galaxies evolve into the spirals and elliptical galaxies that we see today? We describe a mission concept called Galaxy Evolution Spectroscopic Explorer (GESE) to address this question by making a large spectroscopic survey of galaxies at redshift, z~1-2 (lookback times of 8-10 billion years). GESE is a 1.5-m space telescope with a 3-channel multi-object slit spectrograph that can obtain spectra of ~400 galaxies per exposure. Together, the 3 channels cover the spectral range, 0.2-1.6 µm at a resolving power, R~400. (This observed spectral range corresponds to 0.1-0.8 µm in the restframe of a galaxy at a redshift, z=1 galaxy.) The mission concept takes advantage of two new technological advances: (1) light-weighted, wide field of view telescope mirrors, and (2) the Digital Micromirror Device (DMD) to be used as a slit generator in a multichannel (UV, optical, NIR), multi-object slit spectrograph. .

- by Massimo Robberto
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- Physics, Ultraviolet, Galaxy evolution, DMD

We study star formation rates (SFR) and stellar masses in bulges of nearby disk galaxies. For this we construct a new SFR indicator that linearly combines data from Spitzer Space Telescope (SST) and The Galaxy Evolution Explorer (GALEX). All bulges are found to be forming stars irrespective of bulge type (pseudobulge or classical bulge). At present day SFR the median pseudobulge could have grown the present day stellar mass in 8 Gyr. Classical bulges have the lowest specific SFR implying a growth times that are longer than a Hubble time, and thus the present day SFR does not likely play a major role in the evolution of classical bulges. In almost all galaxies in our sample the specific SFR (SFR per unit stellar mass) of the bulge is higher than that of the outer disk. This suggests that almost all galaxies are increasing their B/T through internal star formation. SFR in pseudobulges correlates with their structure. More massive pseudobulges have higher SFR density, this is consistent with that stellar mass being formed by moderate, extended star fromation. Bulges in late-type galaxies have similar SFRs as pseudobulges in intermediate-type galaxies, and are similar in radial size. However, they are deficient in mass; thus, they have much shorter growth times, ∼2 Gyr. We identify a class of bulges that have nuclear morphology similar to pseudobulges, significantly lower specific SFR than pseudobulges, and are closer to classical bulges in structural parameter correlations. These are possibly composite objects, evolved pseudobulges or classical bulges experiencing transient, enhanced nuclear star formation.

The K20 survey is a near infrared-selected, deep (K s < 20) redshift survey targeting galaxies in two independent regions of the sky, the Chandra Deep Field South and the field around the quasar 0055 − 2659, for a total area of 52 arcmin 2 . The total K s -selected sample includes 545 objects. Low-resolution (R ≈ 300 − 600) optical spectra for 525 of them have been obtained with the FORS1/FORS2 spectrographs at the ESO/VLT, providing 501 spectroscopic identifications (including 12 type-1 AGN and 45 stars); consequently, we were able to measure redshifts and identify stars in 96% of the observed objects, whereas the spectroscopic completeness with respect to the total photometrically selected sample is 92% (501/545). The K20 survey is therefore the most complete spectroscopic survey of a near infrared-selected sample to date. The K20 survey contains 444 spectroscopically identified galaxies, covering a redshift range of 0.05 < z < 2.73, with a mean redshift < z >= 0.75; excluding the 32 "low-quality" redshifts does not significantly change these values. This paper describes the final K20 spectroscopic catalogue, along with the technique used to determine redshifts, measure the spectral features and characterize the spectra. The classification of the galaxy spectra has been performed according to a simple parametric recipe that uses the equivalent widths of the two main emission lines ([OII]λ3727 and Hα+ [NII]) and two continuum indices (the 4000Å break index, D4000, and a near-UV color index, C(28-39)). We defined three main spectroscopic classes: red early-type galaxies, blue emission-line galaxies and the intermediate galaxies, which show emission lines but a red continuum. More than 95% of the examined galaxies is included in one of these spectral types and a composite spectrum is built for each of the three galaxy classes. The full spectroscopic catalogue, the reduced individual spectra and the composite spectra are released to the community through the K20 web page (http://www.arcetri.astro.it/ ∼ k20/). The blue emission-line and the early-type galaxies have been divided in redshift bins, and the corresponding composite spectra have been built, in order to investigate the evolution of the spectral properties of the K20 galaxies with redshift. The early-type average spectra are remarkable in their similarity, showing only subtle but systematic differences in the D4000 index, which are consistent with the ageing of the stellar population. Conversely, the star-forming galaxies present a significant "blueing" of the optical/near-UV continuum with redshift, although the [OII] equivalent width remains constant (∼ 33Å) in the same redshift intervals. We reproduce the observed properties with simple, dust-free population synthesis models, suggesting that the highredshift galaxies are younger and more active than those detected at lower redshift, whilst the equivalent width of the emission lines apparently require a lower metallicity for the low-redshift objects. This may be consistent with the metallicity-luminosity relationship locally observed for star-forming galaxies.

We study the feedback from an AGN on stellar formation within its host galaxy, mainly using one high resolution numerical simulation of the jet propagation within the interstellar medium of an early-type galaxy. In particular, we show that in a realistic simulation where the jet propagates into a two-phase ISM, star formation can initially be slightly enhanced and then, on timescales of few million years, rapidly quenched, as a consequence both of the high temperatures attained and of the reduction of cloud mass (mainly due to Kelvin-Helmholtz instabilities). We then introduce a model of (prevalently) negative AGN feedback, where an exponentially declining star formation is quenched, on a very short time scale, at a time t AGN , due to AGN feedback. Using the Bruzual & Charlot (2003) population synthesis model and our star formation history, we predict galaxy colours from this model and match them to a sample of nearby early-type galaxies showing signs of recent episodes of star formation . We find that the quantity t gal − t AGN , where t gal is the galaxy age, is an excellent indicator of the presence of feedback processes, and peaks significantly around t gal − t AGN ≈ 0.85 Gyr for our sample, consistent with feedback from recent energy injection by AGNs in relatively bright (M B ∼ < −19) and massive nearby early-type galaxies. Galaxies that have experienced this recent feedback show an enhancement of 3 magnitudes in N U V (GALEX) − g, with respect to the unperturbed, no-feedback evolution. Hence they can be easily identified in large combined near UV-optical surveys.

- by Vincenzo Antonuccio-Delogu
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- Interstellar Medium, Star Formation, Numerical Simulation, Models

excellent at most wavelengths. The plateau between 1,700 Å and 3,000 Å is due to a local minimum between two broad absorption features caused by amorphous carbon grains, with the added flat contribution from Fe 3 O 4 grains. Silicate... more

- by Stuart Mangles
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- Star Formation, Active Galactic Nuclei, Early Universe, Multidisciplinary
- by Jakob Walcher
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- Interstellar Medium, Star Formation, Molecular Clouds, Ultraviolet