C. Mendes de Oliveira

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.

Intragroup diffuse light in compact groups of galaxies: HCG 79, 88 and 95

Deep B and R images of three Hickson Compact Groups, HCG 79, 88 and 95, have been analysed using a new wavelet technique to measure possible intragroup diffuse light present in these systems. The method used, OV WAV ,i sa wavelet technique particularly suitable for detecting low surface brightness extended structures, down to a signal-to-noise ratio (S/N ) = 0.1 per pixel, which corresponds to a 5σ detection level in wavelet space. The three groups studied are in different evolutionary stages, as can be judged by their very different fractions of the total light contained in their intragroup haloes: 46 ± 11 per cent for HCG 79 and 11 ± 26 per cent for HCG 95, in the B band, and HCG 88 had no component detected down to a limiting surface brightness of 29.1 B mag arcsec −2 .F or HCG 95, the intragroup light (IGL) is red, similar to the mean colours of the group galaxies themselves, suggesting that it is formed by an old population with no significant ongoing star formation. For HCG 79, however, the intragroup material has a significantly bluer colour than the mean colour of the group galaxies, suggesting that the diffuse light may, at least in part, come from stripping of dwarf galaxies which dissolved into the group potential well. Ke yw ords: galaxies: clusters: general ‐ galaxies: evolution ‐ galaxies: interactions ‐ intergalactic medium ‐ dark matter.

GHASP: an Hα kinematic survey of spiral and irregular galaxies – IX. The near-infrared, stellar and baryonic Tully–Fisher relations★

We studied, for the first time, the near-infrared, stellar and baryonic Tully-Fisher relations for a sample of field galaxies taken from a homogeneous Fabry-Perot sample of galaxies [the Gassendi HAlpha survey of SPirals (GHASP) survey]. The main advantage of GHASP over other samples is that the maximum rotational velocities were estimated from 2D velocity fields, avoiding assumptions about the inclination and position angle of the galaxies. By combining these data with 2MASS photometry, optical colours, HI masses and different mass-to-light ratio estimators, we found a slope of 4.48 +/- 0.38 and 3.64 +/- 0.28 for the stellar and baryonic Tully-Fisher relation, respectively. We found that these values do not change significantly when different mass-to-light ratio recipes were used. We also point out, for the first time, that the rising rotation curves as well as asymmetric rotation curves show a larger dispersion in the Tully-Fisher relation than the flat ones or the symmetric ones. Using the baryonic mass and the optical radius of galaxies, we found that the surface baryonic mass density is almost constant for all the galaxies of this sample. In this study we also emphasize the presence of a break in the NIR Tully-Fisher relation at M-H,M-K similar to -20 and we confirm that late-type galaxies present higher total-to-baryonic mass ratios than early-type spirals, suggesting that supernova feedback is actually an important issue in late-type spirals. Due to the well-defined sample selection criteria and the homogeneity of the data analysis, the Tully-Fisher relation for GHASP galaxies can be used as a reference for the study of this relation in other environments and at higher redshifts.

Two formation channels of ultra-compact dwarf galaxies in Hickson compact groups

Context. The formation of ultra-compact dwarf galaxies (UCDs) is believed to be driven by interaction, and UCDs are abundant in the cores of galaxy clusters, environments that mark the end-point of galaxy evolution. Nothing is known about the properties of UCDs in compact groups of galaxies, environments where most of galaxy evolution and interaction is believed to occur and where UCDs in an intermediate stage in their evolution may be expected. Aims. The main goal of this study is to detect and characterize, for the first time, the UCD population of compact groups of galaxies. For that, two nearby groups in different evolutionary stages, HCG 22 and HCG 90, were targeted. Methods. We selected about 40 UCD candidates from pre-existing photometry of both groups, and obtained spectra of these candidates using the VLT FORS2 instrument in MXU mode. Archival HST/ACS imaging was used to measure their structural parameters. Results. We detect 16 and 5 objects belonging to HCG 22 and HCG 90, respectively, covering the magnitude range −10.0 > MR > −11.5 mag. Their integrated colours are consistent with old ages covering a broad range in metallicities (metallicities confirmed by the spectroscopic measurements). Photometric mass estimates put 4 objects in HCG 90 and 9 in HCG 22 in the mass range of UCDs (>2 × 10 6 M� ) for an assumed age of 12 Gyr. These UCDs are on average 2−3 times larger than the typical size of Galactic GCs, covering a range of 2 < rh < 21 pc. The UCDs in HCG 22 are more concentrated around the central galaxy than in HCG 90, at the 99% confidence level. They cover a broad range in [α/Fe] abundances from sub- to super-solar. The spectra of 3 UCDs (2 in HCG 22, 1 in HCG 90) show tentative evidence of intermediate age stellar populations. The clearest example is the largest and most massive UCD (∼10 7 M� ) in our sample, which is detected in HCG 22. Its properties are most consistent with a stripped dwarf galaxy nucleus. We calculate the specific frequency (S N) of UCDs for both groups, finding that HCG 22 has about three times higher S N than HCG 90. Conclusions. The ensemble properties of the detected UCDs supports two co-existing formation channels: a star cluster origin (lowluminosity, compact sizes, old ages, super-solar α/Fe), and an origin as tidally stripped dwarf nuclei (more extended and younger stellar populations). Our results imply that the UCDs detected in both groups do not, in their majority, originate from relatively recent galaxy interactions. Most of the detected UCDs have likely been brought into the group along with their host galaxies.Context. The formation of ultra-compact dwarf galaxies (UCDs) is bel ieved to be interaction driven, and UCDs are abundant in the cores of galaxy clusters, environments that mark the end-po int of galaxy evolution. Nothing is known about the properti s of UCDs in compact groups of galaxies, environments where most of ga laxy evolution and interaction is believed to occur and wher e UCDs in intermediate state of their evolution may be expected. Aims. The main goal of this study is to detect and characterize, for the first time, the UCD population of compact groups of galaxi es. For that, two nearby groups in di fferent evolutionary stages, HCG 22 and HCG 90, were targeted. Methods. We selected about 40 UCD candidates from pre-existing photo metry of both groups, and obtained spectra of these candidates using the VLT FORS2 instrument in MXU mode. Archival HS T/ACS imaging was used to measure their structural parameters . Results. We detect 16 and 5 objects belonging to HCG 22 and HCG 90, respe ctively, covering the magnitude range −10.0 > MR > −11.5 mag. Their integrated colours are consistent with old ages covering a broad range in metallicities (metallicities con firmed by the spectroscopic measurements). Photometric mass estima tes put 4 objects in HCG 90 and 9 in HCG 22 in the mass range of UCD s (> 2 × 10M⊙) for an assumed age of 12 Gyr. These UCDs are on average 2-3 tim es larger than the typical size of Galactic GCs, covering a range of 2. rh . 21 pc. The UCDs in HCG 22 are more concentrated around the cent ral galaxy than in HCG 90, at the 99% confidence level. They cover a broad range in [ α/Fe] abundances from subto super-solar. The spectra of 3 UCD s (2 in HCG 22, 1 in HCG 90) show tentative evidence for intermediate age ste llar populations. The clearest example is the largest and mo st assive UCD (∼ 10M⊙) in our sample, detected in HCG 22. Its properties are most co nsistent with a stripped dwarf galaxy nucleus. We calculate the specific frequency ( S N) of UCDs for both groups, finding that HCG 22 has about three ti m s higherS N than HCG 90. Conclusions. The ensemble properties of the detected UCDs supports two co -existing formation channels: a star cluster origin (lowluminosity, compact sizes, old ages, super-solar α/Fe), and an origin as tidally stripped dwarf nuclei (more ext ended and younger stellar populations). Our results imply that the UCDs detec t d in both groups do not, in their majority, originate from r elatively recent galaxy interactions. Most of the detected UCDs have likely b en brought into the group together with their host galaxies .

The Munich Near-Infrared Cluster Survey: Number Density Evolution of Massive Field Galaxies to z ~ 1.2 as Derived from the K-Band-selected Survey

We derive the number density evolution of massive field galaxies in the redshift range 0.4 < z < 1.2 using the K-band-selected field galaxy sample from the Munich Near-IR Cluster Survey. We rely on spectroscopically calibrated photometric redshifts to determine distances and absolute magnitudes in the rest-frame K band. To assign mass-to-light ratios, we use an approach that maximizes the stellar mass for any K-band luminosity at any redshift. We take the mass-to-light ratio, /LK, of a simple stellar population that is as old as the universe at the galaxys redshift as a likely upper limit. This is the most extreme case of pure luminosity evolution, and in a more realistic model /LK will probably decrease faster with redshift because of increased star formation. We compute the number density of galaxies more massive than 2 × 1010, 5 × 1010, and 1 × 1011 h-2 ☉, finding that the integrated stellar mass function is roughly constant for the lowest mass limit and that it decreases with redshift by a factor of ~3 and by a factor of ~6 for the two higher mass limits, respectively. This finding is in qualitative agreement with models of hierarchical galaxy formation, which predict that the number density of ~M* objects is fairly constant while it decreases faster for more massive systems over the redshift range that our data set probes.

GALAXY EVOLUTION IN A COMPLEX ENVIRONMENT: A MULTI-WAVELENGTH STUDY OF HCG 7*

The environment where galaxies are found heavily influences their evolution. Close groupings, like the ones in the cores of galaxy clusters or compact groups, evolve in ways far more dramatic than their isolated counterparts. We have conducted a multi-wavelength study of Hickson Compact Group 7 (HCG?7), consisting of four giant galaxies: three spirals and one lenticular. We use Hubble Space Telescope (HST) imaging to identify and characterize the young and old star cluster populations. We find young massive clusters (YMCs) mostly in the three spirals, while the lenticular features a large, unimodal population of globular clusters (GCs) but no detectable clusters with ages less than a few Gyr. The spatial and approximate age distributions of the ~300 YMCs and ~150 GCs thus hint at a regular star formation history in the group over a Hubble time. While at first glance the HST data show the galaxies as undisturbed, our deep ground-based, wide-field imaging that extends the HST coverage reveals faint signatures of stellar material in the intragroup medium (IGM). We do not, however, detect the IGM in H I or Chandra X-ray observations, signatures that would be expected to arise from major mergers. Despite this fact, we find that the H I gas content of the individual galaxies and the group as a whole are a third of the expected abundance. The appearance of quiescence is challenged by spectroscopy that reveals an intense ionization continuum in one galaxy nucleus, and post-burst characteristics in another. Our spectroscopic survey of dwarf galaxy members yields a single dwarf elliptical galaxy in an apparent stellar tidal feature. Based on all this information, we suggest an evolutionary scenario for HCG?7, whereby the galaxies convert most of their available gas into stars without the influence of major mergers and ultimately result in a dry merger. As the conditions governing compact groups are reminiscent of galaxies at intermediate redshift, we propose that HCGs are appropriate for studying galaxy evolution at z ~ 1-2.

HIERARCHICAL STRUCTURE FORMATION AND MODES OF STAR FORMATION IN HICKSON COMPACT GROUP 31

The handful of low-mass, late-type galaxies that comprise Hickson Compact Group 31 (HCG 31) is in the midst of complex, ongoing gravitational interactions, evocative of the process of hierarchical structure formation at higher redshifts. With sensitive, multicolor Hubble Space Telescope imaging, we characterize the large population of < 10 Myr old star clusters (SCs) that suffuse the system. From the colors and luminosities of the young SCs, we find that the galaxies in HCG 31 follow the same universal scaling relations as actively star-forming galaxies in the local universe despite the unusual compact group environment. Furthermore, the specific frequency of the globular cluster system is consistent with the low end of galaxies of comparable masses locally. This, combined with the large mass of neutral hydrogen and tight constraints on the amount of intragroup light, indicate that the group is undergoing its first epoch of interaction-induced star formation. In both the main galaxies and the tidal-dwarf candidate, F, stellar complexes, which are sensitive to the magnitude of disk turbulence, have both sizes and masses more characteristic of z = 1-2 galaxies. After subtracting the light from compact sources, we find no evidence for an underlying old stellar population in F—it appears to be a truly new structure. The low-velocity dispersion of the system components, available reservoir of H I, and current star formation rate of ~10 M ☉ yr–1 indicate that HCG 31 is likely to both exhaust its cold gas supply and merge within ~1 Gyr. We conclude that the end product will be an isolated, X-ray-faint, low-mass elliptical.

Intragroup diffuse light in compact groups of galaxies – II. HCG 15, 35 and 51

This continuing study of intragroup light in compact groups of galaxies aims to establish new constraints to models of formation and evolution of galaxy groups, specially of compact groups, which are a key part in the evolution of larger structures, such as clusters. In this paper we present three additional groups (HCG 15, 35 and 51) using deep wide-field B- and R-band images observed with the LAICA camera at the 3.5-m telescope at the Calar Alto observatory (CAHA). This instrument provides us with very stable flat-fielding, a mandatory condition for reliably measuring intragroup diffuse light. The images were analysed with the OV_WAV package, a wavelet technique that allows us to uncover the intragroup component in an unprecedented way. We have detected that 19,15 and 26 per cent of the total light of HCG 15, 35 and 51, respectively, are in the diffuse component, with colours that are compatible with old stellar populations and with mean surface brightness that can be as low as 28.4 B mag arcsec -2 . Dynamical masses, crossing times and mass-to-light ratios were recalculated using the new group parameters. Also tidal features were analysed using the wavelet technique.

DYNAMICAL EFFECTS OF INTERACTIONS AND THE TULLY-FISHER RELATION FOR HICKSON COMPACT GROUPS

We investigate the properties of the B-band Tully-Fisher (T-F) relation for 25 compact group galaxies, using Vmax derived from two-dimensional velocity maps. Our main result is that the majority of the Hickson Compact Group galaxies lie on the T-F relation. However, about 20% of the galaxies, including the lowest-mass systems, have higher B luminosities for a given mass, or alternatively, a mass that is too low for their luminosities. We favor a scenario in which outliers have been brightened because of either enhanced star formation or merging. Alternatively, the T-F outliers may have undergone truncation of their dark halo due to interactions. It is possible that in some cases both effects contribute. The fact that the B-band T-F relation is similar for compact group and field galaxies tells us that these galaxies show common mass-to-size relations and that the halos of compact group galaxies have not been significantly stripped inside R25. We find that 75% of the compact group galaxies studied (22 out of 29) have highly peculiar velocity fields. Nevertheless, a careful choice of inclination, position angle, and center, obtained from the velocity field, and an average of the velocities over a large sector of the galaxy enabled the determination of fairly well-behaved rotation curves for the galaxies. However, two of the compact group galaxies HCG 91a and HCG 96a, which are the most massive members in M51-like pairs, have very asymmetric rotation curves, with one arm rising and the other one falling, indicating most probably a recent perturbation by the small close companions.

Ages, Metallicities, and α-Element Enhancement for Galaxies in Hickson Compact Groups

Central velocity dispersions and eight line-strength Lick indices have been determined from 1.3 A resolution long-slit spectra of 16 elliptical galaxies in Hickson compact groups. These data were used to determine galaxy properties (ages, metallicities, and α-element enhancements) and allowed a comparison with the parameters determined for a sample of galaxies in lower density environments studied by Gonzalez. The stellar population parameters were derived by comparison to single stellar population models of Thomas et al. and to a new set of simple stellar population models for the indices Mg2, Fe5270, and Fe5335 based on synthetic spectra. These models, based on an updated version of the fitting functions presented in Barbuy et al., are fully described here. Our main results are (1) the two samples have similar mean values for the metallicities and [α/Fe] ratios and (2) the majority of the galaxies in compact groups seem to be old (median age of 14 Gyr for eight galaxies for which ages could be derived), in agreement with recent work by Proctor et al. These findings support two possible scenarios: compact groups are either young systems whose members have recently assembled and had not enough time to experience any merging yet, or they are old systems that have avoided merging since their time of formation.