The star formation history of CALIFA galaxies: Radial structures (original) (raw)
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The spatially resolved star formation history of CALIFA galaxies
Astronomy & Astrophysics, 2017
This paper presents the mass assembly time scales of nearby galaxies observed by CALIFA at the 3.5 m telescope in Calar Alto. We apply the fossil record method of the stellar populations to the complete sample of the 3rd CALIFA data release, with a total of 661 galaxies, covering stellar masses from 10 8.4 to 10 12 M and a wide range of Hubble types. We apply spectral synthesis techniques to the datacubes and process the results to produce the mass growth time scales and mass weighted ages, from which we obtain temporal and spatially resolved information in seven bins of galaxy morphology (E, S0, Sa, Sb, Sc, and Sd) and six bins of stellar mass and stellar mass surface density. We use three different tracers of the spatially resolved star formation history (mass assembly curves, ratio of half mass to half light radii, and mass-weighted age gradients) to test if galaxies grow inside-out, and its dependence with galaxy stellar mass, stellar mass surface density, and morphology. Our main results are as follows: (a) the innermost regions of galaxies assemble their mass at an earlier time than regions located in the outer parts; this happens at any given stellar mass (M), stellar mass surface density (Σ), or Hubble type, including the lowest mass systems in our sample. (b) Galaxies present a significant diversity in their characteristic formation epochs for lower-mass systems. This diversity shows a strong dependence of the mass assembly time scales on Σ and Hubble type in the lower-mass range (10 8.4 to 10 10.4), but a very mild dependence in higher-mass bins. (c) The lowest half mass radius (HMR) to half light radius (HLR) ratio is found for galaxies between 10 10.4 and 10 11.1 M , where galaxies are 25% smaller in mass than in light. Low-mass galaxies show the largest ratio with HMR/HLR ∼ 0.89. Sb and Sbc galaxies present the lowest HMR/HLR ratio (0.74). The ratio HMR/HLR is always, on average, below 1, indicating that galaxies grow faster in mass than in light. (d) All galaxies show negative log age M gradients in the inner 1 HLR. The profile flattens (slope less negative) with increasing values of Σ. There is no significant dependence on M within a particular Σ bin, except for the lowest bin, where the gradients becomes steeper. (e) Downsizing is spatially preserved as a function of M and Σ , but it is broken for E and SO where the outer parts are assembled in later epochs than Sa galaxies. These results suggest that independently of their stellar mass, stellar mass surface density, and morphology, galaxies form inside-out on average.
The star formation history of galaxies: the role of galaxy mass, morphology and environment
Monthly Notices of the Royal Astronomical Society, 2015
We analyze the star formation history (SFH) of galaxies as a function of presentday environment, galaxy stellar mass and morphology. The SFH is derived by means of a non-parametric spectrophotometric model applied to individual galaxies at z ∼ 0.04 − 0.1 in the WIde-field Nearby Galaxy-cluster Survey (WINGS) clusters and the Padova Millennium Galaxy and Group Catalogue (PM2GC) field. The field reconstructed evolution of the star formation rate density (SFRD) follows the values observed at each redshift, except at z > 2 where our estimate is ∼ 1.7× higher than the high-z observed value. The slope of the SFRD decline with time gets progressively steeper going from low mass to high mass haloes. The decrease of the SFRD since z = 2 is due to 1) quenching -50% of the SFRD in the field and 75% in clusters at z > 2 originated in galaxies that are passive today -and 2) the fact that the average SFR of today's star-forming galaxies has decreased with time. We quantify the contribution to the SFRD(z) of galaxies of today's different masses and morphologies. The current morphology correlates with the current star formation activity but is irrelevant for the past stellar history. The average SFH depends on galaxy mass, but galaxies of a given mass have different histories depending on their environment. We conclude that the variation of the SFRD(z) with environment is not driven by different distributions of galaxy masses and morphologies in clusters and field, and must be due to an accelerated formation in high mass haloes compared to low mass ones even for galaxies that will end up having the same galaxy mass today.
The Astrophysical Journal, 2007
We derive the luminosity functions of elliptical galaxies, galaxy bulges, galaxy pseudo-bulges and galaxy discs from our structural catalogue of 10,095 galaxies. In addition we compute their associated luminosity and stellar mass densities. We show that spheroidal systems (elliptical galaxies and the bulges of disc galaxies) exhibit a strong color bimodality indicating two distinct types of spheroid which are separated by a core color of (u − r) ∼ 2 mag. We argue that the similarity of the red elliptical and the red bulge luminosity functions supports our previous arguments that they share a common origin and surprisingly find that the same follows for the blue ellipticals and blue bulges, the latter of which we refer to as pseudo-bulges. In terms of the stellar mass budget we find that 58 ± 6 per cent is currently in the form of discs, 39 ± 6 per cent in the form of red spheroids (13 ± 4 per cent ellipticals, 26±4 per cent bulges) and the remainder is in the form of blue spheroidal systems (∼ 1.5 per cent blue ellipticals and ∼ 1.5 per cent pseudo-bulges). In terms of galaxy formation we argue that our data on galaxy components strongly supports the notion of a two-stage formation process (spheroid first, disc later) but with the additional complexity of secular evolution occurring in quiescent discs giving rise to two distinct bulge types: genuine 'classical' bulges and pseudo-bulges. We therefore advocate that there are three significant structures underpinning galaxy evolution: classical spheroids (old); pseudobulges (young) and discs (intermediate). The luminous nearby galaxy population is a mixture of these three structural types. The nature of the blue elliptical galaxies remains unclear but one possibility is that these constitute recently collapsed structures supporting the notion of mass-dependent spheroid formation with redshift.
A comparison of stellar populations in galaxy spheroids across a wide range of Hubble types
Monthly Notices of the Royal Astronomical Society, 2002
We present line-strengths and kinematics from the central regions of 32 galaxies with Hubble types ranging from E to Sbc. Spectral indices, based on the Lick system, are measured in the optical and near infra-red (NIR). The 24 indices measured, in conjunction with models of the effects of varying abundance ratios, permit the breaking of age/metallicity degeneracy and allow estimation of enhancements in specific light elements (particularly C and Mg). The large range of Hubble types observed allows direct comparison of line-strengths in the centres of early-type galaxies (E and S0) with those in spiral bulges, free from systematic differences that have plagued comparisons of results from different studies. Our sample includes field and Virgo cluster galaxies. For early-type galaxies our data are consistent with previously reported trends of Mg 2 and Mgb with velocity dispersion. In spiral bulges we find trends in all indices with velocity dispersion. We estimate luminosity-weighted ages, metallicities and heavy element abundance ratios (enhancements) from optical indices. These show that bulges are less enhanced in light (α-capture) elements and have lower average age than earlytype galaxies. Trends involving age and metallicity also differ sharply between early and late types. An anti-correlation exists between age and metallicity in early types, while, in bulges, metallicity is correlated with velocity dispersion. We consider the implications of these findings for models of the formation of these galaxies. We find that primordial collapse models of galaxy formation are ruled out by our observations, while several predictions of hierarchical clustering (merger) models are confirmed.
Observational tests of the evolution of spheroidal galaxies
Monthly Notices of …, 2005
have elaborated a physically grounded model exploiting the mutual feedback between star-forming spheroidal galaxies and the active nuclei growing in their cores to overcome, in the framework of the hierarchical clustering scenario for galaxy formation, one of the main challenges facing such scenario, i.e. the fact that massive spheroidal galaxies appear to have formed much earlier and faster than predicted by previous semi-analytical models, while the formation process was slower for less massive objects. After having assessed the values of the two parameters that control the effect of the complex and poorly understood radiative transfer processes on the time-dependent spectral energy distributions (SEDs), we have compared the model predictions with a variety of IR to mm data. Our results support a rather strict continuity between objects where stars formed (detected by (sub)-mm surveys) and evolved massive early-type galaxies, indicating that large spheroidal galaxies formed most of their stars when they were already assembled as single objects. The model is remarkably successful in reproducing the observed redshift distribution of K 20 galaxies at z > 1, in contrast with both the classical monolithic models (which overestimate the density at high-z) and the semi-analytic models (that are systematically low), as well as the ratio of star-forming to passively evolving spheroids and the counts and redshift distributions of Extremely Red Objects (EROs), although the need of a more detailed modelling of the star formation history and of dust geometry is indicated by the data. The model also favourably compares with the ISOCAM 6.7 µm counts, with the corresponding redshift distribution, and with Spitzer/IRAC counts, which probe primarily the passive evolution phase, and with the (sub)-mm SCUBA and MAMBO data, probing the active star-formation phase. The observed fraction of 24 µm selected sources with no detectable emission in either the 8 µm or R-band ) nicely corresponds to the predicted surface density of star-forming spheroids with 8 µm fluxes below the detection limit. Finally, distinctive predictions for the redshift distributions of 24 µm sources detected by Spitzer/MIPS surveys are pointed out.
Galaxy And Mass Assembly (GAMA): the Stellar Mass Budget of Galaxy Spheroids and Disks
Monthly Notices of the Royal Astronomical Society, 2016
We build on a recent photometric decomposition analysis of 7506 Galaxy and Mass Assembly (GAMA) survey galaxies to derive stellar mass function fits to individual spheroid and disc component populations down to a lower mass limit of log(M * /M ) = 8. We find that the spheroid/disc mass distributions for individual galaxy morphological types are well described by single Schechter function forms. We derive estimates of the total stellar mass densities in spheroids (ρ spheroid = 1.24 ± 0.49 × 10 8 M Mpc −3 h 0.7 ) and discs (ρ disc = 1.20 ± 0.45 × 10 8 M Mpc −3 h 0.7 ), which translates to approximately 50 per cent of the local stellar mass density in spheroids and 48 per cent in discs. The remaining stellar mass is found in the dwarf 'little blue spheroid' class, which is not obviously similar in structure to either classical spheroid or disc populations. We also examine the variation of component mass ratios across galaxy mass and group halo mass regimes, finding the transition from spheroid to disc mass dominance occurs near galaxy stellar mass ∼10 11 M and group halo mass ∼10 12.5 M h −1 . We further quantify the variation in spheroid-to-total mass ratio with group halo mass for central and satellite populations as well as the radial variation of this ratio within groups.
The effects of star formation history in the SFR–M* relation of H ii galaxies
Monthly Notices of the Royal Astronomical Society
We discuss the implications of assuming different star formation histories (SFH) in the relation between star formation rate (SFR) and mass derived by the spectral energy distribution fitting (SED). Our analysis focuses on a sample of H ii galaxies, dwarf starburst galaxies spectroscopically selected through their strong narrow emission lines in SDSS DR13 at z < 0.4, cross-matched with photometric catalogues from GALEX, SDSS, UKIDSS, and WISE. We modelled and fitted the SEDs with the code CIGALE adopting different descriptions of SFH. By adding information from different independent studies, we find that H ii galaxies are best described by episodic SFHs including an old (10 Gyr), an intermediate age (100−1000 Myr) and a recent population with ages < 10 Myr. H ii galaxies agree with the SFR−M* relation from local star-forming galaxies, and only lie above such relation when the current SFR is adopted as opposed to the average over the entire SFH. The SFR−M* demonstrated not to b...
New Horizon: On the Origin of the Stellar Disk and Spheroid of Field Galaxies at z = 0.7
The Astrophysical Journal
The origin of the disk and spheroid of galaxies has been a key open question in understanding their morphology. Using the high-resolution cosmological simulation, New Horizon, we explore kinematically decomposed disk and spheroidal components of 144 field galaxies with masses greater than 10 9 M at z = 0.7. The origins of stellar particles are classified according to their birthplace (in situ or ex situ) and their orbits at birth. Before disk settling, stars form mainly through chaotic mergers between proto-galaxies and become part of the spheroidal component. When disk settling starts, we find that more massive galaxies begin to form disk stars from earlier epochs; massive galaxies commence to develop their disks at z ∼ 1 − 2, while low-mass galaxies do after z ∼ 1. The formation of disks is affected by accretion as well, as mergers can trigger gas turbulence or induce misaligned gas infall that prevents galaxies from forming co-rotating disk stars. The importance of accreted stars is greater in more massive galaxies, especially in developing massive spheroids. A significant fraction of the spheroids comes from the disk stars that are perturbed, which becomes more important at lower redshifts. Some (∼ 12.5%) of our massive galaxies develop counter-rotating disks from the gas infall misaligned with the existing disk plane, which can last for more than a Gyr until they become the dominant component, and flip the angular momentum of the galaxy in the opposite direction. The final disk-to-total ratio of a galaxy needs to be understood in relation to its stellar mass and accretion history. We quantify the significance of the stars with different origins and provide them as guiding values.
The Astrophysical Journal, 2015
We investigate the cosmic evolution of the black hole (BH) mass-bulge luminosity relation using a sample of 52 active galaxies at z ∼ 0.36 and z ∼ 0.57 in the BH mass range of 10 7.4−9.1 M. By consistently applying multi-component spectral and structural decomposition to high-quality Keck spectra and high-resolution HST images, BH masses (M BH) are estimated using the Hβ broad emission line combined with the 5100 Å nuclear luminosity, and bulge luminosities (L bul) are derived from surface photometry. Comparing the resulting M BH − L bul relation to local active galaxies and taking into account selection effects, we find evolution of the form M BH /L bul ∝ (1+z) γ with γ = 1.8±0.7, consistent with BH growth preceding that of the host galaxies. Including an additional sample of 27 active galaxies with 0.5 < z < 1.9 taken from the literature and measured in a consistent way, we obtain γ = 0.9 ± 0.7 for the M BH − L bul relation and γ = 0.4 ± 0.5 for the M BH-total host galaxy luminosity (L host) relation. The results strengthen the findings from our previous studies and provide additional evidence for host-galaxy bulge growth being dominated by disk-to-bulge transformation via minor mergers and/or disk instabilities.
Astronomy & Astrophysics, 2014
Aims. There are two aims to our analysis. On the one hand we are interested in addressing whether a sample of morphologically selected early-type galaxies (ETGs) differs from a sample of passive galaxies in terms of galaxy statistics. On the other hand we study how the relative abundance of galaxies, the number density, and, the stellar mass density for different morphological types change over the redshift range 0.6 ≤ z ≤ 2.5. Methods. From the 1302 galaxies brighter than Ks(AB)=22 selected from the GOODS-MUSIC catalogue, we classified the ETGs, i.e. elliptical (E) and spheroidal galaxies (E/S0), on the basis of their morphology and the passive galaxies on the basis of their specific star formation rate (sSFR≤10 −11 yr −1 ). Since the definition of a passive galaxy depends on the model parameters assumed to fit the spectral energy distribution of the galaxy, in addition to the assumed sSFR threshold, we probed the dependence of this definition and selection on the stellar initial mass function (IMF). Results. We find that spheroidal galaxies cannot be distinguished from the other morphological classes on the basis of their low star formation rate, irrespective of the IMF adopted in the models. In particular, we find that a large fraction of passive galaxies (> 30 %) are disc-shaped objects and that the passive selection misses a significant fraction (∼ 26 %) of morphologically classified ETGs. Using the sample of 1302 galaxies morphologically classified into spheroidal galaxies (ETGs) and non-spheroidal galaxies (LTGs), we find that the fraction of these two morphological classes is constant over the redshift range 0.6 ≤ z ≤ 2.5, being 20-30 % the fraction of ETGs and 70-80 % the fraction of LTGs. However, at z < 1 these fractions change among the population of the most massive (M * ≥ 10 11 M ⊙ ) galaxies, with the fraction of massive ETGs rising up to 40 % and the fraction of massive LTGs decreasing to 60 %. Parallel to this trend, we find that the number density and the stellar mass density of the whole population of massive galaxies increase by almost a factor of ∼ 10 between 0.6 ≤ z ≤ 2.5, with a faster increase of these densities for the ETGs than for the LTGs. Finally, we find that the number density of the highest-mass galaxies both ETGs and LTGs (M * > 3 − 4 × 10 11 M ⊙ ) does not increase from z ∼ 2.5, contrary to the lower mass galaxies. This suggests that the most massive galaxies formed at z > 2.5 − 3 and that the assembly of such high-mass galaxies is not effective at lower redshift.