Nature or nurture? Clues from the distribution of specific star formation rates in SDSS galaxies (original) (raw)
Related papers
Groups of two galaxies in SDSS: implications of colours on star formation quenching time-scales
Monthly Notices of the Royal Astronomical Society, 2013
We have devised a method to select galaxies that are isolated in their dark matter halo (N = 1 systems) and galaxies that reside in a group of exactly two (N = 2 systems). Our N = 2 systems are widely separated (up to ∼200 h −1 kpc), where close galaxy-galaxy interactions are not dominant. We apply our selection criteria to two volume-limited samples of galaxies from Sloan Digital Sky Survey Data Release 6 (SDSS DR6) with M r − 5 log 10 h ≤ −19 and −20 to study the effects of the environment of very sparse groups on galaxy colour. For satellite galaxies in a group of two, we find a red excess attributed to star formation quenching of 0.15 ± 0.01 and 0.14 ± 0.01 for the −19 and −20 samples, respectively, relative to isolated galaxies of the same stellar mass. Assuming N = 1 systems are the progenitors of N = 2 systems, an immediate-rapid star formation quenching scenario is inconsistent with these observations. A delayed-then-rapid star formation quenching scenario with a delay time of 3.3 and 3.7 Gyr for the −19 and −20 samples, respectively, yields a red excess prediction in agreement with the observations. The observations also reveal that central galaxies in a group of two have a slight blue excess of 0.06 ± 0.02 and 0.02 ± 0.01 for the −19 and −20 samples, respectively, relative to N = 1 populations of the same stellar mass. Our results demonstrate that even the environment of very sparse groups of luminous galaxies influence galaxy evolution and in-depth studies of these simple systems are an essential step towards understanding galaxy evolution in general.
The star formation history of early-type galaxies as a function of mass and environment
Monthly Notices of the Royal Astronomical Society, 2006
Using the third data release of the Sloan Digital Sky Survey (SDSS), we have rigorously defined a volume-limited sample of early-type galaxies in the redshift range 0.005 < z 0.1. We have defined the density of the local environment for each galaxy using a method which takes account of the redshift bias introduced by survey boundaries if traditional methods are used. At luminosities greater than our absolute r-band magnitude cutoff of −20.45, the mean density of environment shows no trend with redshift. We calculate the Lick indices for the entire sample and correct for aperture effects and velocity dispersion in a model-independent way. Although we find no dependence of redshift or luminosity on environment, we do find that the mean velocity dispersion, σ , of early-type galaxies in dense environments tends to be higher than in low-density environments. Taking account of this effect, we find that several indices show small but very significant trends with environment that are not the result of the correlation between indices and velocity dispersion. The statistical significance of the data is sufficiently high to reveal that models accounting only for α-enhancement struggle to produce a consistent picture of age and metallicity of the sample galaxies, whereas a model that also includes carbon enhancement fares much better. We find that early-type galaxies in the field are younger than those in environments typical of clusters but that neither metallicity, α-enhancement nor carbon enhancement are influenced by the environment. The youngest early-type galaxies in both field and cluster environments are those with the lowest σ. However, there is some evidence that the objects with the largest σ are slightly younger, especially in denser environments. Independent of environment both the metallicity and α-enhancement grow monotonically with σ. This suggests that the typical length of the star formation episodes which formed the stars of early-type galaxies decreases with σ. More massive galaxies were formed in faster bursts. We argue that the timing of the process of formation of early-type galaxies is determined by the environment, while the details of the process of star formation, which has built up the stellar mass, are entirely regulated by the halo mass. These results suggest that the star formation took place after the mass assembly and favours an anti-hierarchical model. In such a model, the majority of the mergers must take place before the bulk of the stars form. This can only happen if there exists an efficient feedback mechanism which inhibits the star formation in low-mass haloes and is progressively reduced as mergers increase the mass.
The Astrophysical Journal, 2018
We investigate radial gradients in the recent star formation history (SFH) of low-redshift galaxies using a large sample of 1917 galaxies with 0.01 < z < 0.14 and integral-field spectroscopy from the ongoing Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. For each galaxy, we obtain two-dimensional maps and radial profiles for three spectroscopically-measured parameters that are sensitive to the recent SFH: D n (4000) (the 4000Å break), EW(Hδ A) (equivalent width of the Hδ absorption line), and EW(Hα) (equivalent width of the Hα emission line). We find the majority of the spaxels in these galaxies are consistent with models with continuously declining star formation rate, indicating that starbursts occur rarely in local galaxies with regular morphologies. We classify the galaxies into three classes: fully star-forming (SF), partly quenched (PQ) and totally quenched (TQ), according to the fraction of quenched area within 1.5 times the effective radius, f Q (1.5R e). We find that galaxies less massive than a stellar mass of 10 10 M ⊙ present at most weak radial gradients in all the diagnostic parameters. In contrast, massive galaxies with stellar mass above 10 10 M ⊙ present significant gradients in all the three diagnostic parameters if classified as SF or PQ, but show weak gradients in D n (4000) and EW(Hδ A) and no gradients in EW(Hα) if in the TQ class. This implies the existence of a critical stellar mass, at ∼ 10 10 M ⊙ , above which the star formation in a galaxy gets shutdown from the inside out. Galaxies tend to evolve synchronously from inner to outer regions before their mass reaches the critical value. We have further divided the sample at fixed mass by both bulge-to-total luminosity ratio and morphological type, finding that our conclusions hold regardless of these factors: it appears that the presence of a central dense object like a bulge is not a driving parameter, but rather a byproduct of the star formation cessation process.
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.
Investigating the conclusive phases of galaxy evolution: from star formation to quiescence
2018
Despite the progress made towards a more comprehensive knowledge of galaxy evolution, a global picture of the mechanisms regulating the formation of stars in galaxies, of how galaxy evolutionary properties correlate with stellar masses and star formation rates (SFRs) and of the processes suppressing the star formation in galaxies and their timescales is still lacking. In this thesis work, we attempt to address some of these open questions, inspecting galaxy evolution back in cosmic time. In particular, we start from the archaeological analysis of passive local galaxies (1), reconstructing their past star formation histories. Then we take a step back towards the phase in which galaxies quench their star formation (2), defining a new methodology able to identify the quenching progenitors of passive galaxies. Finally, we move back to the star-forming phase (3), investigating the properties of high-redshift galaxies which could be the star-forming progenitors of the passive local ones. ...
Galaxies in the act of quenching star formation
Monthly Notices of the Royal Astronomical Society, 2018
Detecting galaxies when their star formation is being quenched is crucial to understand the mechanisms driving their evolution. We identify for the first time a sample of quenching galaxies selected just after the interruption of their star formation by exploiting the [O III] λ5007/H α ratio and searching for galaxies with undetected [O III]. Using a sample of ∼174000 star-forming galaxies extracted from the SDSS-DR8 at 0.04 ≤ z< 0.21, weidentify the ∼300 quenching galaxy best candidates with low [O III]/H α, out of ∼26000 galaxies without [O III] emission. They have masses between 10 9.7 and 10 10.8 M , consistently with the corresponding growth of the quiescent population at these redshifts. Their main properties (i.e. star-formation rate, colours, and metallicities) are comparable to those of the star-forming population, coherently with the hypothesis of recent quenching, but preferably reside in higher-density environments. Most candidates have morphologies similar to star-forming galaxies, suggesting that no morphological transformation has occurred yet. From a survival analysis we find a low fraction of candidates (∼0.58 per cent of the star-forming population), leading to a short quenching timescale of t Q ∼ 50 Myr and an e-folding time for the quenching history of τ Q ∼ 90 Myr, and their upper limits of t Q < 0.76 Gyr and τ Q <1.5 Gyr, assuming as quenching galaxies 50 per cent of objects without [O III] (∼7.5 per cent). Ourresults are compatible with a 'rapid' quenching scenario of satellites galaxies due to the final phase of strangulation or ram-pressure stripping. This approach represents a robust alternative to methods used so far to select quenched galaxies (e.g. colours, specific star-formation rate, or post-starburst spectra).
The Star Formation History and Chemical Evolution of Star-Forming Galaxies in the Nearby Universe
The Astrophysical Journal, 2012
We have determined the metallicity (O/H) and nitrogen abundance (N/O) of a sample of 122,751 star-forming galaxies (SFGs) from the Data Release 7 of the Sloan Digital Sky Survey. For all these galaxies we have also determined their morphology and obtained a comprehensive picture of their star formation history (SFH) using the spectral synthesis code STARLIGHT. The comparison of the chemical abundance with the SFH allows us to describe the chemical evolution of the SFGs in the nearby universe (z 0.25) in a manner consistent with the formation of their stellar populations and morphologies. A high fraction (45%) of the SFGs in our sample show an excess abundance of nitrogen relative to their metallicity. We also find this excess to be accompanied by a deficiency of oxygen, which suggests that this could be the result of effective starburst winds. However, we find no difference in the mode of star formation of the nitrogen-rich and nitrogen-poor SFGs. Our analysis suggests that they all form their stars through a succession of bursts of star formation extended over a period of few Gyr. What produces the chemical differences between these galaxies seems therefore to be the intensity of the bursts: the galaxies with an excess of nitrogen are those that are presently experiencing more intense bursts or have experienced more intense bursts in their past. We also find evidence relating the chemical evolution process to the formation of the galaxies: the galaxies with an excess of nitrogen are more massive, and have more massive bulges and earlier morphologies than those showing no excess. Contrary to expectation, we find no evidence that the starburst wind efficiency decreases with the mass of the galaxies. As a possible explanation we propose that the loss of metals consistent with starburst winds took place during the formation of the galaxies, when their potential wells were still building up, and consequently were weaker than today, making starburst winds more efficient and independent of the final mass of the galaxies. In good agreement with this interpretation, we also find evidence consistent with downsizing, according to which the more massive SFGs formed before the less massive ones.
Star formation in distant starburst galaxies
Astronomy and Astrophysics
This paper discusses the stellar population content of distant (5 000 km s −1 ≤ V R ≤ 16 000 km s −1 ) galaxies with enhanced star-formation activity. Distinction is made between isolated galaxies and galaxies morphologically disturbed, with clear signs of interaction such as mergers. In these galaxies the International Ultraviolet Explorer (IUE) large aperture samples most of the galaxy's body. Consequently, the resulting integrated spectra arise primarily from blue stellar populations of different ages together with significant contributions from intermediate and old age components, subject to varying reddening amounts. Instead of analysing individual, usually low Signal-to-Noise ratio (S/N) spectra, our approach is to coadd the spectra of objects with similar spectral properties in the UV, considering as well their properties in the visible/near-infrared ranges. Consequently, the resulting high (S/N) template spectra contain the average properties of a rather uniform class of objects, and information on spectral features can now be analysed with more precision. Three groups have been found for the interacting galaxies, corresponding to a red, blue and very blue continuum. Isolated galaxies have been separated into two groups, one with a flat/red continuum and the other with a blue continuum. For comparison, we also include in the present analysis two groups of nearby disturbed galaxies. Stellar populations are analysed by means of a synthesis algorithm based on star cluster spectral components of different ages which fit the observed spectra both in terms of continuum distribution and spectral features. Flux fractions of the different age groups found in the synthesis have been transformed into mass fractions, allowing inferences on the star formation histories. Young stellar populations (age < 500 Myr) are the main flux contributors, except for the groups with a red spectrum not due to extinction, arising from the intermediate (age ≈ 1 − 2 Gyr) and old age populations. We also study the reddening values and the extinction law: a Small Magellanic Cloud-like extinction law is appropriate for all cases. As compared to nearby galaxies with enhanced star-formation, the distant starburst galaxy spectral groups exhibit larger contributions from the intermediate and old age populations. This effect is mainly accounted for by the larger spatial area sampled Send offprint requests to: C. Bonatto
Morphological quenching of star formation: making early-type galaxies red
2009
We point out a natural mechanism for quenching of star formation in early-type galaxies. It automatically links the color of a galaxy with its morphology and does not require gas consumption, removal or termination of gas supply. Given that star formation takes place in gravitationally unstable gas disks, it can be quenched when a disk becomes stable against fragmentation to bound clumps. This can result from the growth of a stellar spheroid, for instance by mergers. We present the concept of morphological quenching (MQ) using standard disk instability analysis, and demonstrate its natural occurrence in a cosmological simulation using an efficient zoom-in technique. We show that the transition from a stellar disk to a spheroid can be sufficient to stabilize the gas disk, quench star formation, and turn an early-type galaxy red and dead while gas accretion continues. The turbulence necessary for disk stability can be stirred up by sheared perturbations within the disk in the absence of bound star-forming clumps. While other quenching mechanisms, such as gas stripping, AGN feedback, virial shock heating, and gravitational heating are limited to massive halos, the MQ can explain the appearance of red early-type galaxies also in halos less massive than ∼ 10 12 M ⊙ . The dense gas disks observed in some of today's red ellipticals may be the relics of this mechanism, whereas red galaxies with quenched gas disks could be more frequent at high redshift.