IRAC Mid-Infrared Imaging of the Hubble Deep Field-South: Star Formation Histories and Stellar Masses of Red Galaxies at z>2 (original) (raw)
Related papers
Astronomy and Astrophysics, 2007
Context. The classification scheme for high redshift galaxies is complex at the present time, with simple colour selection criteria (i.e. EROs, IEROs, LBGs, DRGs, BzKs), resulting in ill-defined properties regarding stellar mass and star formation rate for these distant galaxies. Aims. The goal of this work is to investigate the properties of different classes of high-z galaxies, focusing in particular on the Stellar Masses of LBGs, DRGs and BzKs, in order to derive their contribution to the total mass budget of the distant Universe. Methods. We have used the GOODS-MUSIC catalog, containing ∼3000 Ks-selected (∼10000 z-selected) galaxies with multiwavelength coverage extending from the U band to the Spitzer 8µm band, with spectroscopic or accurate photometric redshifts. We have selected samples of BM/BX/LBGs, DRGs and BzK galaxies, discussed the overlap and the limitations of these criteria, which can be overcome with a selection criterion based on physical parameters. We have then measured the stellar masses of these galaxies and computed the Stellar Mass Density (SMD) for the different samples up to redshift ≃ 4. Results. We show that the BzK-PE criterion is not optimal to select early type galaxies at the faint end. BzK-SF, on the other hand, is highly contaminated by passively evolving galaxies at red z − Ks colours. We find that LBGs and DRGs contribute almost equally to the global SMD at z ≥ 2 and in general that star forming galaxies form a substantial fraction of the universal SMD. Passively evolving galaxies show a strong negative density evolution from redshift 2 to 3, indicating that we are witnessing the epoch of mass assembly of such objects. Finally we find indications that pushing the selection to deeper magnitudes, the contribution of less massive DRGs could overcome that of LBGs. Deeper surveys, like the HUDF, are required to confirm this suggestion. Conclusions.
Astrophysical Journal, 2005
We combine HST/ACS imaging from the GEMS survey with redshifts and rest-frame quantities from COMBO-17 to study the evolution of morphologically early-type galaxies with red colors since z=1. We use a new large sample of 728 galaxies with centrally-concentrated radial profiles (Sersic n>2.5) and rest-frame U-V colors on the red sequence. By appropriate comparison with the local relations from SDSS, we find that the luminosity-size (L-R) and stellar mass-size (M-R) relations evolve in a manner that is consistent with the passive aging of ancient stars. By itself, this result is consistent with a completely passive evolution of the red early-type galaxy population. If instead, as demonstrated by a number of recent surveys, the early-type galaxy population builds up in mass by a factor of 2 since z=1, our results imply that new additions to the early-type galaxy population follow similar L-R and M-R correlations, compared to the older subset of early-type galaxies. Adding early-type galaxies to the red sequence through disk fading appears to be consistent with the data. Through comparison with models, the role of dissipationless merging is limited to <1 major merger on average since z=1 for the most massive galaxies. Predictions from models of gas-rich mergers are not yet mature enough to allow a detailed comparison to our observations. We find tentative evidence that the amount of luminosity evolution depends on galaxy stellar mass, such that the least massive galaxies show stronger luminosity evolution compared to more massive early types. This could reflect a different origin of low-mass early-type galaxies and/or younger stellar populations; the present data is insufficient to discriminate between these possibilities. (abridged)
Astrophysical Journal, 2004
We recently identified a substantial population of galaxies at z>2 with red rest-frame optical colors. These distant red galaxies (DRGs) are efficiently selected by the simple observed color criterion J-K>2.3. In this paper we present NIR spectroscopy with Keck/NIRSPEC of six DRGs at 2.4<z<3.2. We detect continuum emission and emission lines of all observed galaxies. Equivalent widths of H alpha are 20-30 Ang, smaller than measured for LBGs and nearby LIRGs, and comparable to normal nearby galaxies. The modest equivalent widths imply that the galaxies either have a decreasing star formation rate, or that they are very dusty. Fitting both the photometry and the H alpha lines, we find continuum extinction A_V=1-2 mag, ages 1-2.5 Gyr, star formation rates 200-400 solar masses/yr, and stellar masses 1-5x10^11 solar masses for models with constant star formation rates. From [NII]/H alpha ratios we infer that the metallicities are high, 1-1.5 x Solar. For four galaxies we can determine line widths from the optical emission lines. The widths are high, ranging from 130-240 km/s, and by combining data for LBGs and DRGs we find significant correlations between linewidth and restframe U-V color, and between linewidth and stellar mass. The latter correlation has a similar slope and offset as the ``baryonic Tully-Fisher relation'' for nearby galaxies. The median dynamical mass is ~2x10^11 solar masses, supporting the high stellar masses inferred from the photometry. We find that the median M/L_V ~ 0.8, a factor of ~5 higher than measured for LBGs. We infer from our small sample that DRGs are dustier, more metal rich, more massive, and have higher ages than z=3 LBGs of the same rest-frame V-band luminosity. Their high M/L ratios imply that they contribute significantly to the stellar mass density at z~2.5. [ABRIDGED]
Spitzer Observations of Massive, Red Galaxies at High Redshift
The Astrophysical Journal, 2006
We investigate the properties of massive galaxies at z ∼ 1 − 3.5 using Hubble Space Telescope observations at optical wavelengths, ground-based near-infrared (IR) imaging, and Spitzer Space Telescope observations at 3-24 µm. From K s -selected galaxies over a ≃ 130 arcmin 2 field in the southern Great Observatories Origins Deep Surveys (GOODS-S), we identify 153 distant red galaxies (DRGs) with (J − K s ) Vega ≥ 2.3. This sample is approximately complete in stellar mass for passively evolving galaxies above 10 11 M ⊙ and z ≤ 3. Of the galaxies identified by this selection, roughly half are objects whose optical and near-IR rest-frame light is dominated by evolved stars combined with ongoing star formation (at z med ∼ 2.5), and the others are galaxies whose light is dominated by heavily reddened (A 1600 4 − 6 mag) starbursts (at z med ∼ 1.7). Very few of the galaxies ( 10%) have no indication of current star formation. The total star-formation rates (SFRs) including the reradiated IR emission for the DRGs are up to two orders of magnitude higher than those derived from the UV luminosity corrected for dust reddening. We use population synthesis models to estimate stellar masses and to study the stars that dominate the rest-frame UV through near-IR light in these galaxies. DRGs at z ∼ 1.5 − 3 with stellar masses ≥ 10 11 M ⊙ have specific SFRs (SFRs per unit stellar mass) ranging from 0.2 to 10 Gyr −1 , with a mean value of ∼ 2.4 Gyr −1 . Based on the X-ray luminosities and rest-frame near-IR colors, as many as one-quarter of the DRGs may contain AGN, implying that the growth of supermassive black holes coincides with the formation of massive galaxies at z 1.5. The DRGs with M ≥ 10 11 M ⊙ at 1.5 ≤ z ≤ 3 have integrated specific SFRs greater the global value over all galaxies at this epoch. In contrast, we find that galaxies at z ∼ 0.3 − 0.75 with M ≥ 10 11 M ⊙ have integrated specific SFRs less than the global value, and more than an order of magnitude lower than that for massive DRGs at z ∼ 1.5 − 3. At z 1, lower-mass galaxies dominate the overall cosmic mass assembly. This suggests that the bulk of star formation in massive galaxies occurs at early cosmic epochs and is largely complete by z ∼ 1.5. Further mass assembly in these galaxies takes place with low specific SFRs.
Astrophysical Journal, 2004
We investigate the nature of the substantial population of high-z galaxies with Js-Ks>2.3 discovered as part of our FIRES survey. This colour cut efficiently isolates z>2 galaxies with red rest-frame optical colors ("Distant Red Galaxies" or DRGs). We select objects in the 2.5'x2.5' HDF-South (HDF-S) and 5'x5' field around the MS1054-03 cluster; the surface densities at Ks<21 are 1.6+-0.6 and 1.0+-0.2 arcmin^-2. We discuss the 34 DRGs at 2<z<3.5: 11 at Ks<22.5 in HDF-S and 23 at Ks<21.7 in the MS1054-03 field. We analyze the SEDs constructed from our deep near-infrared (NIR) and optical imaging from the ESO VLT and HST. We develop diagnostics involving I-Js, Js-H, and H-Ks to argue that the red NIR colors of DRGs cannot be attributed solely to extinction and require for many an evolved stellar population with prominent Balmer/4000A break. In the rest-frame, the optical colours of DRGs fall within the envelope of normal nearby galaxies and the UV colours suggest a wide range in star formation activity and/or extinction. This contrasts with the much bluer and more uniform SEDs of Lyman break galaxies (LBGs). From evolutionary synthesis models with constant star formation, solar metallicity, Salpeter IMF, and Calzetti et al. extinction law, we derive for the HDF-S (MS1054-03 field) DRGs median ages of 1.7(2.0) Gyr, A_V = 2.7(2.4) mag, stellar masses 0.8(1.6)x10^11 Msun, M/L_V = 1.2(2.3) Msun/LVsun, and SFR = 120(170) Msun/yr. Models assuming declining SFRs with e-folding timescales of 10Myr-1Gyr generally imply younger ages, lower A_V's and SFRs, but similar stellar masses within a factor of two. Compared to LBGs at similar redshifts and rest-frame L_V's, DRGs are older, more massive, and more obscured for any given star formation history. [ABRIDGED]
Astrophysical Journal, 2008
Using a sample of ∼28,000 sources selected at 3.6-4.5 microns with Spitzer observations of the HDF-N, the CDF-S, and the Lockman Hole (surveyed area: ∼664 arcmin 2 ), we study the evolution of the stellar mass content of the Universe at 0<z<4. We calculate stellar masses and photometric redshifts, based on ∼2,000 templates built with stellar population and dust emission models fitting the UV-to-MIR spectral energy distributions of galaxies with spectroscopic redshifts. We estimate stellar mass functions for different redshift intervals. We find that 50% of the local stellar mass density was assembled at 0<z<1 (average SFR: 0.048 M ⊙ yr −1 Mpc −3 ), and at least another 40% at 1<z<4 (average SFR: 0.074 M ⊙ yr −1 Mpc −3 ). Our results confirm and quantify the "downsizing" scenario of galaxy formation. The most massive galaxies (M>10 12.0 M ⊙ ) assembled the bulk of their stellar content rapidly (in 1-2 Gyr) beyond z∼3 in very intense star formation events (producing high specific SFRs). Galaxies with 10 11.5 <M<10 12.0 M ⊙ assembled half of their stellar mass before z∼1.5, and more than 90% of their mass was already in place at z∼0.6. Galaxies with M<10 11.5 M ⊙ evolved more slowly (presenting smaller specific SFRs), assembling half of their stellar mass below z∼1. About 40% of the local stellar mass density of 10 9.0 <M<10 11.0 M ⊙ galaxies was assembled below z∼0.4, most probably through accretion of small satellites producing little star formation. The cosmic stellar mass density at z>2.5 is dominated by optically faint (R 25) red galaxies (Distant Red Galaxies or BzK sources) which account for ∼30% of the global population of galaxies, but contribute at least 60% to the cosmic stellar mass density. Bluer galaxies (e.g., Lyman Break Galaxies) are more numerous but less massive, contributing less than 50% to the global stellar mass density at high redshift.
The 2dF-SDSS LRG and QSO Survey: the star formation histories of luminous red galaxies
Monthly Notices of the Royal Astronomical Society, 2006
We present a detailed investigation into the recent star formation histories of 5,697 Luminous Red Galaxies (LRGs) based on the Hδ(4101Å), and [O ii] (3727Å) lines and the D4000 index. LRGs are luminous (L> 3L*), galaxies which have been selected to have photometric properties consistent with an old, passively evolving stellar population. For this study we utilise LRGs from the recently completed 2dF-SDSS LRG and QSO survey (2SLAQ). Equivalent widths of the Hδ and [O ii] lines are measured and used to define three spectral types, those with only strong Hδ absorption (k+a), those with strong [O ii] in emission (em) and those with both (em+a). All other LRGs are considered to have passive star formation histories. The vast majority of LRGs are found to be passive (∼80 per cent), however significant numbers of k+a (2.7 per cent), em+a (1.2 per cent) and em LRGs (8.6 per cent) are identified. An investigation into the redshift dependence of the fractions is also performed. A sample of SDSS MAIN galaxies with colours and luminosities consistent with the 2SLAQ LRGs is selected to provide a low redshift comparison. While the em and em+a fractions are consistent with the low redshift SDSS sample, the fraction of k+a LRGs is found to increase significantly with redshift. This result is interpreted as an indication of an increasing amount of recent star formation activity in LRGs with redshift. By considering the expected life time of the k+a phase, the number of LRGs which will undergo a k+a phase can be estimated. A crude comparison of this estimate with the predictions from semi-analytic models of galaxy formation shows that the predicted level of k+a and em+a activity is not sufficient to reconcile the predicted mass growth for massive early-types in a hierarchical merging scenario.
The Optical and Near-Infrared Properties of Galaxies. I. Luminosity and Stellar Mass Functions
The Astrophysical …, 2003
We use a large sample of galaxies from the Two Micron All Sky Survey (2MASS) and the Sloan Digital Sky Survey (SDSS) to calculate galaxy luminosity and stellar mass functions in the local Universe. We estimate corrections for passband shifting and galaxy evolution, as well as present-day stellar mass-to-light (M/L) ratios, by fitting the optical-near-infrared galaxy data with simple models. Accounting for the 8% galaxy overdensity in the SDSS early data release region, the optical and near-infrared luminosity functions we construct for this sample agree with most recent literature optical and near-infrared determinations within the uncertainties. We argue that 2MASS is biased against low surface brightness galaxies, and use SDSS plus our knowledge of stellar populations to estimate the 'true' K-band luminosity function. This has a steeper faint end slope and a slightly higher overall luminosity density than the direct estimate. Furthermore, assuming a universally-applicable stellar initial mass function (IMF), we find good agreement between the stellar mass function we derive from the 2MASS/SDSS data and that derived by Cole et al. (2001; MNRAS, 326, 255). The faint end slope slope for the stellar mass function is steeper than −1.1, reflecting the low stellar M/L ratios characteristic of low-mass galaxies. We estimate an upper limit to the stellar mass density in the local Universe Ω * h = 2.0 ± 0.6 × 10 −3 by assuming an IMF as rich in low-mass stars as allowed by observations of galaxy dynamics in the local Universe. The stellar mass density may be lower than this value if a different IMF with fewer low-mass stars is assumed. Finally, we examine typedependence in the optical and near-infrared luminosity functions and the stellar mass function. In agreement with previous work, we find that the characteristic luminosity or mass of early-type galaxies is larger than for later types, and the faint end slope is steeper for later types than for earlier types. Accounting for typing uncertainties, we estimate that at least half, and perhaps as much as 3/4, of the stellar mass in the Universe is in early-type galaxies. As an aid to workers in the field, we present in an appendix the relationship between model stellar M/L ratios and colors in SDSS/2MASS passbands, an updated discussion of near-infrared stellar M/L ratio estimates, and the volume-corrected distribution of g and K-band stellar M/L ratios as a function of stellar mass.
Star-forming Galaxies at Intermediate Redshifts: Morphology, Ages, and Sizes
The Astronomical Journal, 2006
We present the analysis of the deepest near-UV image obtained with Hubble Space Telescope using the WFPC2(F300W) as part of the parallel observations of the Hubble Ultra Deep Field campaign. The U-band 10σ limiting magnitude measured over 0.2 arcsec 2 is m AB =27.5 which is 0.5 magnitudes deeper than that in the Hubble Deep Field North. We matched the U-band catalog with those in the ACS images (B, V, i, z) taken during the Great Observatories Origins Deep Survey observations of the Chandra Deep Field South and obtained photometric redshifts for 306 matched objects. We find that the UV-selected galaxies span all the major morphological types at 0.2 <z phot < 1.2. However, disks are more common at lower redshifts, 0.2 <z phot < 0.8. Higher redshift objects (0.7 <z phot < 1.2) are on average bluer than lower−z and have spectral type typical of starbursts. Their morphologies are compact, peculiar or low surface brightness galaxies. Despite the UV-selection, 13 objects have spectral types of early-type galaxies; two of them are spheroids with blue cores. The evolutionary synthesis code, Starburst99, was used to age-date the UV-selected galaxies which were found to have rest-frame colors typical of stellar populations with intermediate ages > 100 Myr. The average halflight radius (rest-frame 1200-1800Å) of the UV-selected galaxies at 0.66<z phot <1.5 is 0.26 ± 0.01 arcsec (2.07 ± 0.08 kpc). The UV-selected galaxies are on average fainter (M B =-18.43±0.13) than Lyman Break Galaxies (M B =-23±1). Our sample includes early-type galaxies that are presumably massive and forming stars only in their cores, as well as starburst-type systems that are more similar to the LBGs, although much less luminous. This implies that even the starbursts in our sample are either much less massive than LBGs or are forming stars at a much lower rate or both. The low surface brightness galaxies have no overlap with the LBGs and form an interesting new class of their own.
The Astrophysical Journal, 2006
As part of the DEEP2 galaxy redshift survey, we analyze absorption line strengths in stacked Keck/DEIMOS spectra of red field galaxies with weak to no emission lines, at redshifts 0.7 ≤ z ≤ 1. Comparison with models of stellar population synthesis shows that red galaxies at z ∼ 0.9 have mean luminosity-weighted ages of the order of only 1 Gyr and at least solar metallicities. This result cannot be reconciled with a scenario where all stars evolved passively after forming at very high z. Rather, a significant fraction of stars can be no more than 1 Gyr old, which means that star formation continued to at least z ∼ 1.2. Furthermore, a comparison of these distant galaxies with a local SDSS sample, using stellar populations synthesis models, shows that the drop in the equivalent width of Hδ from z ∼ 0.9 to 0.1 is less than predicted by passively evolving models. This admits of two interpretations: either each individual galaxy experiences continuing low-level star formation, or the red-sequence galaxy population from z ∼ 0.9 to 0.1 is continually being added to by new galaxies with younger stars.