D. Mehlert

Spatially resolved spectroscopy of Coma cluster early-type galaxies - III. The stellar population gradients

Based on Paper I of this series (Mehlert et al. 2000), we derive central values and logarithmic gradients for the H, Mg and Fe indices of 35 early-type galaxies in the Coma cluster. We find that pure elliptical galaxies have on average slightly higher velocity dispersions, lower H, and higher metallic line-strengths than galaxies with disks (S0). The latter form two families, one comparable to the ellipticals and a second one with significantly higher H, and weaker metallic lines. Our measured logarithmic gradients within the eective radius areh4Mg b i 0:037,h4hFeii 0:029,h4H i+0:017 and h4i 0:063. The gradients strongly correlate with the gradients of , but only weakly with the central index values and galaxy velocity dispersion. Using stellar population models with variable element abundance ratios from Thomas et al. (2003a) we derive average ages, metallicities and (=Fe) ratios in the center and at the eective radius. We find that the =Fe ratio correlates with velocity dispersion and drives 30% of the Mg- relation, the remaining 70% being caused by metallicity variations. We confirm previous findings that part of the lenticular galaxies in the Coma cluster host very young (2 Gyr) stellar populations, hence must have experienced relatively recent star formation episodes. Again in accordance with previous work we derive negative metallicity gradients ( 0:16 dex per decade) that are significantly flatter than what is expected from gaseous monolithic collapse models, pointing to the importance of mergers in the galaxy formation history. Moreover, the metallicity gradients correlate with the velocity dispersion gradients, confirming empirically earlier suggestions that the metallicity gradient in ellipticals is produced by the local potential well. The gradients in age are negligible, implying that no significant residual star formation has occurred either in the center or in the outer parts of the galaxies, and that the stellar populations at dierent radii must have formed at a common epoch. For the first time we derive the gradients of the =Fe ratio and find them very small on average. Hence, =Fe enhancement is not restricted to galaxy centers but it is a global phenomenon. Our results imply that the Mg- local relation inside a galaxy, unlike the global Mg- relation, must be primarily driven by metallicity variations alone. Finally we note that none of the stellar population parameters or their gradients depend on the density profile of the Coma cluster, even though it spans 3 dex in density.

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.

Lyα emission in high-redshift galaxies ⋆

Context. A significant fraction of the high-redshift galaxies show st rong Lyα emission lines. For redshifts z> 5, most known galaxies belong to this class. However, so far not much is known about the physical structure and nature of these objects. Aims. Our aim is to analyse the Lyα emission in a sample of high-redshift UV-continuum selected galaxies and to derive the physical conditions that determine the Lyα profile and the line strength. Methods. VLT/FORS spectra with a resolution of R≈ 2000 of 16 galaxies in the redshift range of z = 2.7 to 5 are presented. The observed Lyα profiles are compared with theoretical models. Results. The Lyα lines range from pure absorption (EW = -17 A) to strong emission (EW = 153 A). Most Lyα emission lines show an asymmetric profile, and three galaxies have a double-peaked profile. Both types of profiles can be explained by a uniform mo del consisting of an expanding shell of neutral and ionised hydrogen around a compact starburst region. The broad, blueshifted, low-ionisation interstellar absorption lines indicate a galaxy-scale outflow of the ISM. The strengths of these lines are found to be determined in part by the velocity dispersion of the outflowing medium. We find star-formation r ates of these galaxies ranging from S FRUV = 1.2 to 63.2 M⊙yr −1 uncorrected for dust absorption. Conclusions. The Lyα emission strength of our target galaxies is found to be deter mined by the amount of dust and the kinematics of the outflowing material.

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.

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 nature of the Lyα-emission region of FDF-4691

In order to study the origin of the strong Lyman-alpha emission of high-redshift starburst galaxies we observed and modeled the emission of the z = 3.304 galaxy FDF-4691 (rest-frame EW = 103 Angstroem). The observations show that FDF-4691 is a young starburst galaxy with a (for this redshift) typical metallicity. The broad, double-peaked profile of the Lyman-alpha emission line can be explained assuming a highly turbulent emission region in the inner part of the starburst galaxy, and a surrounding extended shell of low-density neutral gas with a normal dust/gas ratio and with Galactic dust properties. The detection of the Lyman-alpha emission line is explained by the intrinsic broad Lyman-alpha emission and a low HI column density of the neutral shell. A low dust/gas ratio in the neutral shell is not needed to explain the strong Lyman-alpha line.

Gravitationally Lensed High Redshift Galaxies in the Field of 1E0657-56

We present images and long-slit spectra obtained with FORS1 at UT1 of the VLT centered on the gravitational arc of the galaxy cluster 1E0657-56 (z =0 :296). The cluster is one of the hottest, most massive clusters known so far and acts as a powerful gravitational telescope, amplifying the flux of background sources by up to a factor of 20. We present photometric results together with the spectra of the gravitational arc (z =3 :24) and four additional amplied high redshift objects (z =2 :34 to 3.08) that were also included in the slit by chance coincidence. A magnication map has been obtained from a lens model derived from the multiple image systems. We compare our observed spectra with models and briefly discuss the stellar contents of these galaxies. Furthermore we measured the equivalent widths of the C iv 1550 and Si iv 1400 absorption lines for the objects behind 1E0657-56 studied here, as well as for some additional starburst galaxies (nearby and at high z). For C iv we nd an increasing absorption equivalent width with decreasing redshift. We discuss whether this correlation could be related to the increase of metallicity with the age of the universe.

Spatially resolved spectroscopy of Coma cluster early-type galaxies - II. The minor axis dataset

We present minor axis, offset major axis and one diagonal long slit spectra for 10 E and SO galaxies of the Coma cluster drawn from a magnitude-limited sample studied before. We derive rotation curves, velocity dispersionprofiles and the H 3 and H 4 coefficients of the Hermite decomposition of the line of sight velocity distribution. Moreover, we derive the line index profiles of Mg, Fe and Hβ line indices and assess their errors. The data will be used to construct dynamical models of the galaxies and study their stellar populations.