Armin Gabasch

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.

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.

The Tully-Fisher relation at intermediate redshift

Using the Very Large Telescope in Multi Object Spectroscopy mode, we have observed a sample of 113 field spiral galaxies in the FORS Deep Field (FDF) with redshifts in the range 0.1< z< 1.0. The galaxies were selected based on apparent brightness (R< 23 m ) and encompass all late spectrophotometric types from Sa to Sdm/Im. Spatially resolved rotation curves have been extracted for 77 galaxies and fitted with synthetic velocity fields taking into account all observational e ffects from inclination and slit misalignment to seeing and slit width. We also compared different shapes for the intrinsic rotation curve. To obtain robust values of Vmax, our analysis is focused on galaxies with rotation curves th at extend well into the region of constant rotation velocity at large radii. If the slope of th e local Tully-Fisher relation (TFR) is held fixed, we find evid ence for a mass-dependent luminosity evolution which is as large as up toMB≈ −2 m for the lowest-mass galaxies, but is small or even negligible for the highest-mass systems in our sample. In effect, the TFR slope is shallower at z≈ 0.5 in comparison to the local sample. We argue for a mass-dependent evolution of the mass-to-light ratio. An additional population of blue, low-mass spirals does not seem a very appealing explanation. The flatter tilt we find for the distant TFR is in contradictio n to the predictions of recent semi-analytic simulations.

THE EVOLUTION OF EARLY- AND LATE-TYPE GALAXIES IN THE COSMIC EVOLUTION SURVEY UP TO z ≈ 1.2*

The Cosmic Evolution Survey (COSMOS) allows for the first time a highly significant census of environments and structures up to redshift 1, as well as a full morphological description of the galaxy population. In this paper we present a study aimed to constrain the evolution, in the redshift range 0.2 7 × 1010 M ☉) early-type galaxies have similar characteristic ages, colors, and SSFRs independently of the environment they belong to, with those hosting the oldest stars in the universe preferentially belonging to the highest density regions. The whole catalog including morphological information and stellar mass estimates analyzed in this work is made publicly available.

The Evolution of the Tully-Fisher Relation of Spiral Galaxies*

We present the B-band Tully-Fisher relation (TFR) of 60 late-type galaxies with redshifts 0.1–1. The galaxies were selected from the FORS Deep Field with a limiting magnitude of . Spatially resolved rotation curves R p 23 were derived from spectra obtained with FORS2 at the Very Large Telescope. High-mass galaxies with vmax 150 km s 1 show little evolution, whereas the least massive systems in our sample are brighter by ∼1–2 mag compared with their local counterparts. For the entire distant sample, the TFR slope is flatter than for local field galaxies ( vs. ). Thus, we find evidence for the evolution of the slope of the TFR 5.77 0.45 7.92 0.18 with redshift on the 3 j level. This is still true when we subdivide the sample into three redshift bins. We speculate that the flatter tilt of our sample is caused by the evolution of luminosities and an additional population of blue galaxies at . The mass dependence of the TFR evolution also leads to variations for different z 0.2 galaxy types in magnitude-limited samples, suggesting that selection effects can account for the discrepant results of previous TFR studies on the luminosity evolution of late-type galaxies. Subject headings: galaxies: evolution — galaxies: kinematics and dynamics — galaxies: spiral

The FORS Deep Field: Field selection, photometric observations and photometric catalog ,

The FORS Deep Field project is a multi-colour, multi-object spectroscopic investigation of a ∼7 � × 7 � region near the south galactic pole based mostly on observations carried out with the FORS instruments attached to the VLT telescopes. It includes the QSO Q 0103-260 (z = 3.36). The goal of this study is to improve our understanding of the formation and evolution of galaxies in the young Universe. In this paper the field selection, the photometric observations, and the data reduction are described. The source detection and photometry of objects in the FORS Deep Field is discussed in detail. A combined B and I selected UBgRIJKsphotometric catalog of 8753 objects in the FDF is presented and its properties are briefly discussed. The formal 50% completeness limits for point sources, derived from the co-added images, are 25.64, 27.69, 26.86, 26.68, 26.37, 23.60 and 21.57 in U, B, g, R, I, J and Ks(Vega-system), respectively. A comparison of the number counts in the FORS Deep Field to those derived in other deep field surveys shows very good agreement.

The FORS Deep Field spectroscopic survey

We present a catalogue and atlas of low-resolution spectra of a well defined sample of 341 objects in the FORS Deep Field. All spectra were obtained with the FORS instruments at the ESO VLT with essentially the same spectroscopic set-up. The observed extragalactic objects cover the redshift range 0. 1t o 5.0. 98 objects are starburst galaxies and QSOs at z > 2. Using this data set we investigated the evolution of the characteristic spectral properties of bright starburst galaxies and their mutual relations as a function of redshift. Significant evolutionary effects were found for redshifts 2 < z < 4. Most conspicuous are the increase of the average C IV absorption strength, of the dust reddening, and of the intrinsic UV luminosity, and the decrease of the average Lyα emission strength with decreasing redshift. In part the observed evolutionary effects can be attributed to an increase of the metallicity of the galaxies with cosmic age. Moreover, the increase of the total star-formation rates and the stronger obscuration of the starburst cores by dusty gas clouds suggest the occurrence of more massive starbursts at later cosmic epochs.

The evolution of the mass function split by morphology up to redshift 1 in the FORS deep and the GOODS-S fields

We study the evolution of the stellar mass density for the separate families of bulge-dominated and disk-dominated galaxies over the redshift range . We derive quantitative morphology for a statistically significant 0.25 ≤ z ≤ 1.15 galaxy sample of 1645 objects selected from the FORS Deep Field and the GOODS-S field. We find that the morphological mix evolves monotonically with time: the higher the redshift, the more disk systems dominate the total mass content. At , massive objects ( ) host about half of the mass contained in objects 10 z ∼ 1 M ≥ 7 # 10 M ∗ , of similar mass in the local universe. The contribution from early- and late-type galaxies to the mass budget at is nearly equal. We show that in situ star formation is not sufficient to explain the changing mass budget. z ∼ 1 Moreover, we find that the star formation rate per unit stellar mass of massive galaxies increases with redshift only for the intermediate and early morphological types while it stays nearly constant for late-type objects. This suggests that merging and/or frequent accretion of small-mass objects has a key role in the shaping of the Hubble sequence as we observe it now and also in decreasing the star formation activity of the bulge-dominated descendants of massive disk galaxies. Subject headings: cosmology: observations — galaxies: evolution — galaxies: formation — galaxies: fundamental parameters — galaxies: luminosity function, mass function — surveys

Lyα emission galaxies at a redshift of z 5.7 in the FORS Deep Field

Context. We present the results of a search for Lyα emission galaxies at z≈ 5.7 in the FORS Deep Field. Aims. The objective of this study is to improve the faint end of the l uminosity function of high-redshift Lyα emitting galaxies and to derive properties of intrinsically faint Lyα emission galaxies in the young universe. Methods. Using FORS2 at the ESO VLT and a set of special interference fil ters, we identified candidates for high-redshift Lyα galaxies. We then used FORS2 in spectroscopic mode to verify the identific ations and to study their spectral properties. Results. The narrow-band photometry resulted in the detection of 15 likely Lyα emission galaxies. Spectra with an adequate exposure time could be obtained for eight galaxies . In all these cases the p resence of Lyα emission at z = 5.7 was confirmed spectroscopically. The line fluxes of the 15 candidates range between 3× 10 −21 Wm −2 and 16× 10 −21 Wm −2 , which corresponds to star-formation rates not corrected f or dust between 1 and 5 M⊙yr −1 . The luminosity function derived for our photometrically identified objects extends the published luminosity functio ns of intrinsically brighter Lyα galaxies. Conclusions. With this technique the study of high-redshift Lyα emission galaxies can be extended to low intrinsic luminosities.

The star formation rate history in the fors deep and goods-south fields

We measure the star formation rate (SFR) as a function of redshift z up to z ≈ 4.5, based on B-, I-, and (I+B)-selected galaxy catalogs from the FORS Deep Field (FDF) and the K-selected catalog from the GOODS-South field. Distances are computed from spectroscopically calibrated photometric redshifts accurate to Δz/(zspec + 1) ≤ 0.03 for the FDF and ≤0.056 for the GOODS-South field. The SFRs are derived from the luminosities at 1500 A. We find that the total SFR estimates derived from B, I, and I+B catalogs agree very well (0.1 dex), while the SFR from the K catalog is lower by ≈0.2 dex. We show that the latter is due solely to the lower star-forming activity of K-selected intermediate- and low-luminosity (L L*) galaxies is independent of the selection band, i.e., the same for B-, I-, (I+B)-, and K-selected galaxy samples. At all redshifts, luminous galaxies (L > L*) contribute only approximately one-third to the total SFR. There is no evidence for significant cosmic variance between the SFRs in the FDF and in the GOODS-South field, 0.1 dex, consistent with theoretical expectations. The SFRs derived here are in excellent agreement with previous measurements, provided that we assume the same faint-end slope of the luminosity function as previous works (α ~ -1.6). However, our deep FDF data indicate a shallower slope of α = -1.07, implying a SFR lower by ≈0.3 dex. We find the SFR to be roughly constant up to z ≈ 4 and then to decline slowly beyond, if dust extinctions are assumed to be constant with redshift.