G. Feulner

The Munich Near-Infrared Cluster Survey (MUNICS). VI. The Stellar Masses of K-Band-selected Field Galaxies to z ~ 1.2

We present a measurement of the evolution of the stellar mass function in four redshift bins at 0.4 0 to estimates obtained similarly at z = 0. We find that the mass-to-light ratios in the K band decline with redshift. This decline is similar for all stellar masses above 1010 h-2 M☉. Lower mass galaxies have lower mass-to-light ratios at all redshifts. The stellar mass function evolves significantly to z = 1.2. The total normalization decreases by a factor of ~2, the characteristic mass (the knee) shifts toward lower masses, and the bright end therefore steepens with redshift. The amount of number density evolution is a strong function of stellar mass, with more massive systems showing faster evolution than less massive systems. We discuss the total stellar mass density of the universe and compare our results to the values from the literature at both lower and higher redshifts. We find that the stellar mass density at z ~ 1 is roughly 50% of the local value. Our results imply that the mass assembly of galaxies continues well after z ~ 1. Our data favor a scenario in which the growth of the most massive galaxies is dominated by accretion and merging rather than star formation, which plays a larger role in the growth of less massive systems.

Extremely compact massive galaxies at z ∼ 1.4

The optical rest-frame sizes of 10 of the most massive (∼5 × 10 11 h −2 M� ) galaxies found in the near-infrared MUNICS survey at 1.2 < z < 1.7 are analysed. Sizes are estimated in both the J and Kfilters. These massive galaxies are at least a factor of 4 +1.9 (±1σ ) smaller in the rest-frame V-band than local counterparts of the same stellar mass. Consequently, the stellar mass density of these objects is (at least) 60 times larger than that of massive ellipticals today. Although the stellar populations of these objects are passively fading, their structural properties are rapidly changing since that redshift. This observational fact disagrees with a scenario where the more massive and passive galaxies are fully assembled at z ∼ 1.4 (i.e. a monolithic scenario) and points towards a dry merger scenario as the responsible mechanism for the subsequent evolution of these galaxies.

The Stellar Mass Function of Galaxies to z ~ 5 in the FORS Deep and GOODS-South Fields

We present a measurement of the evolution of the stellar mass function (MF) of galaxies and the evolution of the total stellar mass density at 0 1010 M☉, which are the likely progenitors of todays L > L* galaxies, are found in much smaller numbers above z ~ 2. However, we note that massive galaxies with M > 1011 M☉ are present even to the largest redshift we probe. Beyond z ~ 2, the evolution of the MF becomes more rapid. We find that the total stellar mass density at z = 1 is 50% of the local value. At z = 2, 25% of the local mass density is assembled, and at z = 3 and z = 5, we find that at least 15% and 5% of the mass in stars is in place, respectively. The number density of galaxies with M > 1011 M☉ evolves very similarly to the evolution at lower masses. It decreases by 0.4 dex to z ~ 1, by 0.6 dex to z ~ 2, and by 1 dex to z ~ 4.

The Kormendy relation of massive elliptical galaxies at z∼ 1.5: evidence for size evolution

We present the morphological analysis based on HST-NIC2 (0.075 arcsec pixel -1 ) images in the F160W filter of a sample of nine massive field (>10 11 M ⊙ ) galaxies spectroscopically classified as early-types at 1.2 < z < 1.7. Our analysis shows that all of them are bulge-dominated systems. In particular, six of them are well fitted by a de Vaucouleurs profile (n = 4) suggesting that they can be considered pure elliptical galaxies. The remaining three galaxies are better fitted by a Sersic profile with index 1.9 < n fit < 2.3 suggesting that a disc-like component could contribute up to 30 per cent to the total light of these galaxies. We derived the effective radius R e and the mean surface brightness (SB) (μ) e within R e of our galaxies and we compared them with those of early-types at lower redshifts. We find that the SB (μ) e of our galaxies should get fainter by 2.5 mag from z ∼ 1.5 to ∼0 to match the SB of the local ellipticals with comparable R e , that is, the local Kormendy relation. Luminosity evolution without morphological changes can only explain half of this effect, as the maximum dimming expected for an elliptical galaxy is ∼ 1.6 mag in this redshift range. Thus, other parameters, possibly structural, may undergo evolution and play an important role in reconciling models and observations. Hypothesizing an evolution of the effective radius of galaxies we find that R e should increase by a factor of 1.5 from z ∼ 1.5 to ∼0.

Specific Star Formation Rates to Redshift 5 from the FORS Deep Field and the GOODS-S Field*

We explore the buildup of stellar mass in galaxies over the wide redshift range 0.4 < z < 5.0 by studying the evolution of the specific star formation rate (SSFR), defined as the star formation rate per unit stellar mass, as a function of stellar mass and age. Our work is based on a combined sample of ~9000 galaxies from the FORS Deep Field and the GOODS-S field, providing high statistical accuracy and relative insensitivity against cosmic variance. As at lower redshifts, we find that lower mass galaxies show higher SSFRs than higher mass galaxies, although highly obscured galaxies remain undetected in our sample. Furthermore, the highest mass galaxies contain the oldest stellar populations at all redshifts, in principle agreement with the existence of evolved, massive galaxies at 1 < z < 3. It is remarkable, however, that this trend continues to very high redshifts of z ~ 4. We also show that with increasing redshift, the SSFR for massive galaxies increases by a factor of ~10, reaching the era of their formation at z ~ 2 and beyond. These findings can be interpreted as evidence for an early epoch of star formation in the most massive galaxies and for ongoing star formation activity in lower mass galaxies.

Specific star formation rates to redshift 1.5

We present a study to determine how star formation contributes to galaxy growth since z = 1.5 over five decades in galaxy stellar mass. We investigate the specific star formation rate (SSFR; star formation rate [SFR] per unit galaxy stellar mass) as a function of galaxy stellar mass and redshift. A sample of 175 K-band-selected galaxies from the MUnich Near-Infrared Cluster Survey spectroscopic data set provides intermediate- to high-mass galaxies (mostly M* ≥ 1010 M☉) to z = 1. The FORS Deep Field provides 168 low-mass galaxies (mostly M* ≤ 1010 M☉) to z = 1.5. We use a Sloan Digital Sky Survey galaxy sample to test the compatibility of our results with data drawn from a larger volume. We find that at all redshifts, the SSFR decreases with increasing galaxy stellar mass, suggesting that star formation contributes more to the growth of low-mass galaxies than to the growth of high-mass galaxies and that high-mass galaxies formed the bulk of their stellar content before z = 1. At each epoch, we find a ridge in SSFR versus stellar mass that is parallel to lines of constant SFR and evolves independently of galaxy stellar mass to a particular turnover mass. Galaxies above this turnover mass show a sharp decrease in the SFR compared to the average at each epoch, and the turnover mass increases with redshift. The SFR along the SSFR ridge decreases by roughly a factor of 10, from 10 M☉ yr-1 at z = 1.5 to 1 M☉ yr-1 at z = 0. High-mass galaxies could sustain the observed rates of star formation over the 10 Gyr observed, but low-mass galaxies likely undergo episodic starbursts.

The density of very massive evolved galaxies to z ≃ 1.7

We spectroscopically identified seven massive, evolved galaxies with magnitudes 17.8 2 supporting a high efficiency in the accretion of the stellar mass in massive haloes in the early Universe.

The Munich near-infrared cluster survey - I.:field selection, object extraction and photometry

The Munich Near-Infrared Cluster Survey (MUNICS) is a wide-area, medium-deep, photometric survey selected in the K′ band. It covers an area of roughly 1 deg2 in the K′ and J near-IR passbands. The survey area consists of 16 6×6 arcmin2 fields targeted at QSOs with redshifts 0.5<z<2 and seven 28×13 arcmin2 strips targeted at ‘random’ high Galactic latitude fields. 10 of the QSO fields were additionally imaged in R and I, and 0.6 deg2 of the randomly selected fields were also imaged in the V, R and I bands. The resulting object catalogues were strictly selected in K′, having a limiting magnitude (50 per cent completeness) of K′∼19.5 mag and J∼21 mag, sufficiently deep to detect passively evolving systems up to a redshift of z≲1.5 and luminosity of 0.5L*. The optical data reach a depth of roughly R∼23.5 mag. The main scientific aims of the project are the identification of galaxy clusters at redshifts around unity and the selection of a large sample of field early-type galaxies at 0<z<1.5 for evolutionary studies. In this paper – the first in a series – we describe the concept of the survey, the selection of the survey fields, the near-IR and optical imaging and data reduction, object extraction, and the construction of photometric catalogues. Finally, we show the J−K′ versus K′ colour–magnitude diagram and the R−J versus J−K′, V−I versus J−K′, and V−I versus V−R colour–colour diagrams for MUNICS objects, together with stellar population synthesis models for different star formation histories, and conclude that the data set presented is suitable for extracting a catalogue of massive field galaxies in the redshift range 0.5≲z≲1.5 for evolutionary studies and follow-up observations.

The extraordinarily bright optical afterglow of GRB 991208 and its host galaxy

Broad-band optical observations of the extraordi- narily bright optical afterglow of the intense gamma-ray burst GRB 991208 started � 2.1 days after the event and continued until 4 Apr 2000. The flux decay constant of the optical after- glow in the R-band is 2.30 ± 0.07 up to � 5 days, which

The Munich Near-Infrared Cluster Survey. II. The K-Band Luminosity Function of Field Galaxies to z ~ 1.2

We present a measurement of the evolution of the rest-frame K-band luminosity function to z ~ 1.2 using a sample of more than 5000 K-selected galaxies drawn from the Munich Near-Infrared Cluster Survey (MUNICS) data set. Distances and absolute K-band magnitudes are derived using photometric redshifts from spectral energy distribution fits to BVRIJK photometry. These are calibrated using more than 500 spectroscopic redshifts. We obtain redshift estimates having an rms scatter of 0.055 and no mean bias. We use Monte Carlo simulations to investigate the influence of the errors in distance associated with photometric redshifts on our ability to reconstruct the shape of the luminosity function. Finally, we construct the rest-frame K-band LF in four redshift bins spanning 0.4 < z < 1.2 and compare our results to the local luminosity function. We discuss and apply two different estimators to derive likely values for the evolution of the number density, Φ*, and characteristic luminosity, M*, with redshift. While the first estimator relies on the value of the luminosity function binned in magnitude and redshift, the second estimator uses the individually measured {M, z} pairs alone. In both cases we obtain a mild decrease in number density by ~25% to z = 1, accompanied by brightening of the galaxy population by 0.5-0.7 mag. These results are fully consistent with an analogous analysis using only the spectroscopic MUNICS sample. The total K-band luminosity density is found to scale as d log ρL/dz = 0.24. We discuss possible sources of systematic errors and their influence on our parameter estimates. By comparing the luminosity density and the cumulative redshift distributions of galaxies in single survey fields to the sample averages, we show that cosmic variance is likely to significantly influence infrared selected samples on scales of ~100 arcmin2.