arXiv subjects

B. L. Ziegler

Publications and source records attributed to B. L. Ziegler.

At least 19 recordsLinked to original sources

arXiv2025

The BLOBs: Enigmatic Diffuse Ionized Gas Structures in a Cluster of Galaxies near Cosmic Noon

We explore the massive cluster XMMXCS J2215.9-1738 at z about 1.46 with MUSE and KMOS integral field spectroscopy. Using MUSE spectroscopy we traced the kinematics of the ionized gas using [OII] in the central 500x500 square kpc area of the cluster, which contains 28 spectroscopically identified cluster galaxies. We detected [OII] emission lines in the integrated spectra of 21 galaxies. The remaining seven are passive galaxies. Six of these passive galaxies lie in the central part of the cluster, which has a diameter of 200 kpc and which contains no star-forming objects. In this place star-formation in galaxies is quenched. An interesting discovery in this central area of the cluster are three diffuse ionized [OII] gas structures, which we refer to as [OII] blobs. They extend over areas of some hundred square kpc. The ionization source of one of the gaseous structures that displays two prominent filamentary patterns indicating outflow of gas is an active galactic nucleus (AGN). The KMOS data enabled us to use the BPT diagram to identify this object as a type 2 AGN. The other two diffuse ionized oxygen gaseous structures are more enigmatic. They are located between the stellar components of passive cluster galaxies. One of these blobs lacks a stellar counterpart in the HST optical and near-infrared data, and the other blob has only a very faint counterpart. Ram-pressure stripping of photoionized gas or AGN feedback might be an explanation. Additionally, the galaxy velocity distribution in this high-redshift cluster is bimodal, which indicates that the cluster is probably not fully virialized and that recent and ongoing merging events that produced shocks might provide photoionization sources for the two enigmatic [OII] blobs.

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arXiv2022

Morpho-kinematics of MACS J0416.1-2403 low mass galaxies

We use optical spectroscopy from VLT/MUSE, as well as photometric observations from HST and VLT/HAWK-I, to study the morpho-kinematics of 17 low mass MACS J0416.1-2403 cluster galaxies at R200 and 5 field galaxies with a redshift of z~0.4. By measuring fluxes of emission lines, we have recovered the star formation rates, gas-phase metallicities and the spatially resolved gas kinematics. We have analysed the structure and morphology of the galaxies from the photometric data, performing a multi-component decomposition into a bulge and a disk. The spatially resolved gas velocity fields were modelled using a 3D approach, which allowed us to retrieve their intrinsic gas kinematics, including the maximum rotation velocity and velocity dispersion. The cluster and field population can be classified as star forming main-sequence galaxies, with only a sub-sample of 4 quenched systems. The lowest mass systems deviate from the predictions of the fundamental metallicity relation, showing higher metallicities, whereas the higher mass ones are in accordance with the model predictions. This might hint at the cut-off of pristine gas inflow and/or the removal of the hot halo gas as the mechanisms driving these offsets. Our morpho-kinematic analysis reveals a sub-sample of dwarfs with maximum velocities vmax <50 km/s, which depart from the Tully-Fisher relation. This might indicate that their interstellar medium is affected by ram pressure stripping. However, ~30% of the cluster galaxies have rotation-dominated gas disks and follow the Tully-Fisher relation. In the stellar mass-S0.5 plane, the systems follow a tight sequence, with only a sub-population of 5 galaxies strongly departing from this relation. Both the morphology and kinematics of the outlier galaxies hint at a combination of pre-processing and cluster-specific interactions affecting their stellar and gas disks.

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arXiv2021

Star-formation quenching of cluster galaxies as traced by metallicity, presence of active galactic nuclei, and galactic conformity

(Abridged) We explored 18 clusters from LoCuSS at z~0.2 with ACReS spectra of ~1800 cluster members at R<R200 in a mass-complete sample. The metallicities of SF cluster galaxies with R<R200 were found to be enhanced with respect to the MZR of coeval field SF galaxies. This metallicity enhancement is limited to lower-mass satellites of the 9 clusters with a passive BCG. Many of the SF galaxies with enhanced metallicities are found in the core regions of the phase-space diagram expected for virialized populations. We find a higher fraction of higher mass SF galaxies at R<R500 in clusters with active BCGs compared to clusters with passive BCGs, a signal for galactic conformity. In contrast, much higher fractions of AGNs and especially recently quenched galaxies (RQGs) at R<R500 are found in clusters with passive BCGs in comparison to clusters with active BCGs. We deduce that strangulation is initiated in clusters with passive BCGs when SF satellite galaxies pass R200, by stopping the pristine gas inflow which would otherwise dilute the ISM and would maintain their metallicities at values similar to those of field galaxies at similar redshifts. For galaxies with higher masses which survived to be SF when travelling to R<R500 of clusters with passive BCGs, we assume that they suffer a rapid quenching of star formation, likely due to AGNs triggered by the increasing RPS toward the cluster center, which can compress the gas and fuel AGNs; these AGNs can rapidly quench and maintain quenched satellite galaxies. On the other hand, we found that surviving SF massive satellite galaxies around active BCGs are less affected by environment when they enter R<R500, since we observe R<R500 SF galaxies with higher masses and with metallicities typical of coeval field galaxies. This observed galactic conformity implies that active BCGs must maintain their activity over timescales of at least ~1Gyr.

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arXiv2021

The VLT-MUSE and ALMA view of the MACS 1931.8-2635 brightest cluster galaxy

We reveal the importance of ongoing in-situ star formation in the Brightest Cluster Galaxy in the massive cool-core CLASH cluster MACS 1931.8-2635 at z=0.35. Using a multi-wavelength approach, we assess the stellar and warm ionized medium components, spatially resolved by the VLT-MUSE spectroscopy, and link them to the molecular gas by incorporating sub-mm ALMA observations. We measure the fluxes of strong emission lines, allowing us to determine the physical conditions of the warm ionized gas. The ionized gas flux brightness peak corresponds to the location of the supermassive black hole and the system shows a diffuse warm ionized gas tail extending 30 kpc in N-E direction. The ionized and molecular gas are co-spatial and co-moving, with the gaseous component in the tail falling inward, providing fuel for star formation and accretion-powered nuclear activity. The gas is ionized by a mix of star formation and other energetic processes which give rise to LINER-like emission, with active galactic nuclei emission dominant only in the BCG core. We measure a star formation rate of 97 Msun/yr, with its peak at the BCG core. However, star formation accounts for only 50-60% of the energetics needed to ionize the warm gas. In situ star formation generated by thermally unstable intracluster medium cooling and/or dry mergers dominate the stellar mass growth at z<0.5 and these mechanisms account for the build-up of 20% of the mass of the system. Our measurements reveal that the most central regions of the BCG contain the lowest gas phase oxygen abundance, whereas the tail exhibits slightly more elevated values. The galaxy is a dispersion dominated system, typical for massive, elliptical galaxies. The gas and stellar kinematics are decoupled, with the gaseous velocity fields being more closely related to the bulk motions of the intracluster medium.

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arXiv2019

Kinematics of disk galaxies in (proto-)clusters at z=1.5

We observed star-forming galaxies at z~1.5 selected from the HyperSuprimeCam Subaru Strategic Program. The galaxies are part of two significant overdensities of [OII] emitters identified via narrow-band imaging and photometric redshifts from grizy photometry. We used VLT/KMOS to carry out Halpha integral field spectroscopy of 46 galaxies in total. Ionized gas maps, star formation rates and velocity fields were derived from the Halpha emission line. We quantified morphological and kinematical asymmetries to test for potential gravitational (e.g. galaxy-galaxy) or hydrodynamical (e.g. ram-pressure) interactions. Halpha emission was detected in 36 targets. 34 of the galaxies are members of two (proto-)clusters at z=1.47, confirming our selection strategy to be highly efficient. By fitting model velocity fields to the observed ones, we determined the intrinsic maximum rotation velocity Vmax of 14 galaxies. Utilizing the luminosity-velocity (Tully-Fisher) relation, we find that these galaxies are more luminous than their local counterparts of similar mass by up to ~4 mag in the rest-frame B-band. In contrast to field galaxies at z<1, the offsets of the z~1.5 (proto-)cluster galaxies from the local Tully-Fisher relation are not correlated with their star formation rates but with the ratio between Vmax and gas velocity dispersion sigma_g. This probably reflects that, as is observed in the field at similar redshifts, fewer disks have settled to purely rotational kinematics and high Vmax/sigma_g ratios. Due to relatively low galaxy velocity dispersions (sigma_v < 400 km/s) of the (proto-)clusters, gravitational interactions likely are more efficient, resulting in higher kinematical asymmetries, than in present-day clusters. (abbr.)

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arXiv2019

CLASH-VLT: Enhancement of (O/H) in z=0.35 RXJ 2248-4431 cluster galaxies

(Abridged) We explore the Frontier Fields cluster RXJ2248-443 at z~0.35 with VIMOS/VLT spectroscopy from CLASH-VLT, which covers a central region corresponding to almost 2 virial radii. The fluxes of [OII], Hbeta, [OIII], Halpha and [NII] emission lines were measured allowing the derivation of (O/H) gas metallicities, star formation rates based on extinction-corrected Halpha fluxes and active galactic nuclei (AGN) contamination. We compare our sample of cluster galaxies to a population of field galaxies at similar redshifts. We use the location of galaxies in projected phase-space to distinguish between cluster and field galaxies. Both populations follow the star-forming-sequence in the diagnostic diagrams, which allow disentangling between the ionising sources in a galaxy, with only few galaxies classified as Seyfert II. Both field and cluster galaxies follow the "Main-Sequence" of star forming galaxies, with no substantial difference observed between the two populations. In the Mass - Metallicity (MZ) plane, both high mass field and cluster galaxies show comparable (O/H)s to the local SDSS MZ relation, with an offset of low mass galaxies towards higher metallicities. While both the metallicities of "accreted" (R < R500) and "infalling" (R > R500) cluster members are comparable at all masses, the cluster galaxies from the intermediate, mass complete bin show more enhanced metallicities than their field counterparts. The intermediate mass field galaxies are in accordance with the expected (O/H)s from the Fundamental Metallicity relation, while the cluster members deviate strongly from the model predictions. The results of this work are in accordance with studies of other clusters at z < 0.5 and favour the scenario in which the hot halo gas of log(M/Msun)<10.2 cluster galaxies is removed due to mild ram pressure stripping, leading to an increase in their gas-phase metallicity.

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arXiv2019

Cluster induced quenching of galaxies in the massive cluster XMMXCSJ2215.9-1738 at z~1.5 traced by enhanced metallicities inside half R200

(Abridged) We explore the massive cluster XMMXCSJ2215.9-1738 at z~1.5 with KMOS spectroscopy of Halpha and [NII] covering a region that corresponds to about one virial radius. Using published spectroscopic redshifts of 108 galaxies in and around the cluster we computed the location of galaxies in the projected velocity vs. position phase-space to separate our cluster sample into a virialized region of objects accreted longer ago (roughly inside half R200) and a region of infalling galaxies. We measured oxygen abundances for ten cluster galaxies with detected [NII] lines in the individual galaxy spectra and compared the MZR of the galaxies inside half R200 with the infalling galaxies and a field sample at similar redshifts. We find that the oxygen abundances of individual z~1.5 star-forming cluster galaxies inside half R200 are comparable, at the respective stellar mass, to the higher local SDSS metallicity values. We find that the [NII]/Halpha line ratios inside half R200 are higher by 0.2 dex and that the resultant metallicities of the galaxies in the inner part of the cluster are higher by about 0.1 dex, at a given mass, than the metallicities of infalling galaxies and of field galaxies at z~1.5. The enhanced metallicities of cluster galaxies at z~1.5 inside half R200 indicate that the density of the ICM in this massive cluster becomes high enough toward the cluster center such that the ram pressure exceeds the restoring pressure of the hot gas reservoir of cluster galaxies. This can remove the gas reservoir initiating quenching; although the galaxies continue to form stars, albeit at slightly lower rates, using the available cold gas in the disk which is not stripped.

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arXiv2018

Slow-then-rapid quenching as traced by tentative evidence for enhanced metallicities of cluster galaxies at z~0.2 in the slow quenching phase

(Abridged) We explore 7 clusters from LoCuSS at z~0.2 with spectra of 1965 cluster members from the ACReS Hectospec survey covering a region which corresponds to about three virial radii for each cluster. We measure fluxes of five emission lines of cluster members enabling us to unambiguously derive O/H gas metallicities, and also SFRs from extinction corrected Halpha fluxes. We compare our cluster galaxy sample with a field sample of 705 galaxies at similar redshifts observed with Hectospec. We find that star-forming cluster and field galaxies show similar median specific SFRs in a given mass bin, but their O/H values are displaced to higher values at projected radii of R<R200 compared with galaxies at larger radii and in the field. The comparison with metallicity-SFR-mass model predictions with inflowing gas indicates a slow-quenching scenario in which strangulation is initiated when galaxies pass R~R200 by stopping the inflow of gas. The metallicities of cluster members inside R200 are thereby increasing, but their SFRs are hardly affected for a period of time, because these galaxies consume available disk gas. We use the fraction of star-forming cluster galaxies as a function of clustercentric radius compared to predictions from the Millennium simulation to constrain quenching timescales to be 1-2Gyrs. This is consistent with a slow-then-rapid quenching scenario. Slow quenching (strangulation) starts when the gas inflow is stopped when the galaxy passes R200 with a phase in which cluster galaxies are still star-forming, but they show elevated metallicities tracing the ongoing quenching. This phase lasts for 1-2Gyrs, meanwhile the galaxies travel to denser inner regions of the cluster, and is followed by a "rapid" phase: a rapid complete quenching of star formation due to the increasing ram-pressure towards the cluster center which can also strip the cold gas in massive galaxies.

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arXiv2018

Unveiling the dynamical state of massive clusters through the ICL fraction

We have selected a sample of eleven massive clusters of galaxies observed by the Hubble Space Telescope in order to study the impact of the dynamical state on the IntraCluster Light (ICL) fraction, the ratio of total integrated ICL to the total galaxy member light. With the exception of the Bullet cluster, the sample is drawn from the Cluster Lensing and Supernova Survey and the Frontier Fields program, containing five relaxed and six merging clusters. The ICL fraction is calculated in three optical filters using the CHEFs IntraCluster Light Estimator, a robust and accurate algorithm free of a priori assumptions. We find that the ICL fraction in the three bands is, on average, higher for the merging clusters, ranging between $\sim7-23\%$, compared with the $\sim 2-11\%$ found for the relaxed systems. We observe a nearly constant value (within the error bars) in the ICL fraction of the regular clusters at the three wavelengths considered, which would indicate that the colors of the ICL and the cluster galaxies are, on average, coincident and, thus, their stellar populations. However, we find a higher ICL fraction in the F606W filter for the merging clusters, consistent with an excess of lower-metallicity/younger stars in the ICL, which could have migrated violently from the outskirts of the infalling galaxies during the merger event.

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arXiv2017

CLASH-VLT: Strangulation of cluster galaxies in MACSJ0416.1-2403 as seen from their chemical enrichment

(abridged) We explore the Frontier Fields cluster MACS J0416.1-2403 at z=0.3972 with VIMOS/VLT spectroscopy from the CLASH-VLT survey covering a region which corresponds to almost three virial radii. We measure fluxes of 5 emission lines of 76 cluster members enabling us to unambiguously derive O/H gas metallicities, and also SFRs from Halpha. For intermediate massses we find a similar distribution of cluster and field galaxies in the MZR and mass vs. sSFR diagrams. Bulge-dominated cluster galaxies have on average lower sSFRs and higher O/Hs compared to their disk-dominated counterparts. We use the location of galaxies in the projected velocity vs. position phase-space to separate our cluster sample into a region of objects accreted longer time ago and a region of recently accreted and infalling galaxies. We find a higher fraction of accreted metal-rich galaxies (63%) compared to the fraction of 28% of metal-rich galaxies in the infalling regions. Intermediate mass galaxies falling into the cluster for the first time are found to be in agreement with predictions of the fundamental metallicity relation. In contrast, for already accreted star-forming galaxies of similar masses, we find on average metallicities higher than predicted by the models. This trend is intensified for accreted cluster galaxies of the lowest mass bin, that display metallicities 2-3 times higher than predicted by models with primordial gas inflow. Environmental effects therefore strongly influence gas regulations and control gas metallicities of log(M/Msun)<10.2 (Salpeter IMF) cluster galaxies. We also investigate chemical evolutionary paths of model galaxies with and without inflow of gas showing that strangulation is needed to explain the higher metallicities of accreted cluster galaxies. Our results favor a strangulation scenario in which gas inflow stops for log(M/Msun)<10.2 galaxies when accreted by the cluster.

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arXiv2015

The mass-metallicity relation of zCOSMOS galaxies at z ~ 0.7, its dependence on SFR, and the existence of massive low-metallicity galaxies

(Abridged) The knowledge of the number and of the physical nature of low-metallicity massive galaxies is crucial for the determination and interpretation of the mass-metallicity relation (MZR). Using VLT-ISAAC near-infrared (NIR) spectroscopy of 39 zCOSMOS z~0.7 galaxies, we have measured Halpha and [NII] emission line fluxes for galaxies with [OII], Hbeta and [OIII] available from VIMOS optical spectroscopy. The NIR spectroscopy enables us to break the degeneracy of the R23 method to derive unambiguously O/H gas metallicities, and also SFRs from extinction corrected Halpha. Using, as a benchmark, the position in the D4000 vs. [OIII]/Hbeta diagram of galaxies with reliable O/Hs from NIR spectroscopy, we were able to break the lower/upper branch R23 degeneracy of additional 900 zCOSMOS z~0.7 galaxies. Additionally, the Halpha-based SFR measurements were used to find the best SFR calibration based on [OII] for the zCOSMOS z~0.7 galaxies without Halpha measurements. We find a fraction of 19% of lower mass 9.5<logM/Msun<10.3 zCOSMOS galaxies which shows a larger evolution of the MZR relation, compared to higher mass galaxies, being more metal poor at a given mass by a factor of 2-3 compared to SDSS. This indicates that the low-mass MZR slope is getting steeper at z~0.7 compared to local galaxies. The existence of these metal-poor galaxies at z~0.7 can be interpreted as the chemical version of galaxy downsizing. Moreover, the sample of zCOSMOS galaxies shows direct evidence that SFR influences the MZR at these redshifts. The comparison of the measured metallicities for the zCOSMOS sample with the values expected for a non-evolving fundamental metallicity relation (FMR) shows broadly agreement, and reveals that also galaxies with lower metallicities and typically higher (specific) SFRs, as found in our zCOSMOS sample at z~0.7, are in agreement with the predictions of a non-evolving Z(M,SFR).

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arXiv2014

Oxygen abundances of zCOSMOS galaxies at z~1.4 based on five lines and implications for the fundamental metallicity relation

A relation between the stellar mass M and the gas-phase metallicity Z of galaxies, the MZR, is observed up to higher redshifts. It is a matter of debate, however, if the SFR is a second parameter in the MZR. To explore this issue at z > 1, we used VLT-SINFONI near-infrared (NIR) spectroscopy of eight zCOSMOS galaxies at 1.3 < z < 1.4 to measure the strengths of four emission lines: Hbeta, [OIII]lambda5007, Halpha, and [NII]lambda6584, additional to [OII]lambda3727 measured from VIMOS. We derive reliable O/H metallicities based on five lines, and also SFRs from extinction corrected Halpha measurements. We find that the MZR of these star-forming galaxies at z~1.4 is lower than the local SDSS MZR by a factor of three to five, a larger change than reported in the literature using [NII]/Halpha-based metallicities from individual and stacked spectra. Correcting N2-based O/Hs using recent results by Newman et al. (2014), also the larger FMOS sample at z~1.4 of Zahid et al. (2014) shows a similar evolution of the MZR like the zCOSMOS objects. These observations seem also in agreement with a non-evolving FMR using the physically motivated formulation of the FMR from Lilly et al. (2013).

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arXiv2011

The Cosmic Web and galaxy evolution around the most luminous X-ray cluster: RXJ1347.5-1145

In this paper we study the large scale structures and their galaxy content around the most X-ray luminous cluster known, RX J1347.5-1145 at z=0.45. We make use of ugriz CFHT MEGACAM photometry and VIMOS VLT spectroscopy to identify structures around the RXJ1347 on a scale of 20x20 Mpc2. We construct maps of the galaxy distribution and the fraction of blue galaxies. We study the photometric galaxy properties as a function of environment, traced by the galaxy density. We identify group candidates based on galaxy overdensities and study their galaxy content. We also use available GALEX NUV imaging to identify strong unobscured star forming galaxies. We find that the large scale structure around RXJ1347 extends in the NE-SW direction for at least 20 Mpc, in which most of the group candidates are located. As other studies, we find that the fraction of blue galaxies (Fblue) is a function of galaxy number density, but the bulk of the trend is due to galaxies belonging to massive systems. The fraction of the UV-bright galaxies is also function of environment, but their relative numbers compared to the blue population seems to be constant regardless of the environment. These UV emitters also have similar properties at all galaxy densities, indicating that the transition between galaxy types occurs in short time-scales. Candidate galaxy groups show a large variation in their galaxy content and Fblue in those groups display little dependence with galaxy density. This may indicate possible differences in their evolutionary status or the processes that are acting in groups are different than in clusters. The large scale structure around rich clusters are dynamic places for galaxy evolution. In the case of RXJ1347 the transformation may start within infalling groups to finish with the removal of the cold gas once galaxies are accreted in massive systems. (ABRIDGED)

astro-ph.CO↗

arXiv2010

Two formation channels of UCDs in Hickson Compact Groups

The formation of ultra-compact dwarf galaxies (UCDs) is believed to be interaction driven, 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 intermediate state of evolution may be expected. The main goal of this study is to detect and characterize, for the first time, the UCD population of compact groups. For that, 2 groups in different evolutionary stages, HCG 22 and HCG 90, were targeted with VLT/FORS2/MXU. We detect 16 and 5 objects belonging to HCG 22 and HCG 90, respectively, covering the magnitude range -10.0 > M_R > -11.5 mag. Their colours are consistent with old ages covering a broad range in metallicities. Photometric mass estimates put 4 objects in HCG 90 and 9 in HCG 22 in the mass range of UCDs (>2x10^6 M_Sun) for an assumed age of 12 Gyr. These UCDs are on average 2-3 times larger than typical Galactic GCs, covering a range of 2 >~ r_h >~ 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 [alpha/Fe] abundances from sub- to super-solar. The spectra of 3 UCDs show tentative evidence for intermediate age stellar populations. 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. The ensemble properties of the detected UCDs supports 2 co-existing formation channels: a star cluster origin and an origin as tidally stripped dwarf nuclei. 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 with their host galaxies.[abridged]

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arXiv2008

Internal kinematics of spiral galaxies in distant clusters III. Velocity fields from FORS2/MXU spectroscopy

(Abridged) We study the impact of cluster environment on the evolution of spiral galaxies by examining their structure and kinematics. Rather than two-dimensional rotation curves, we observe complete velocity fields by placing three adjacent and parallel FORS2 MXU slits on each object, yielding several emission and absorption lines. The gas velocity fields are reconstructed and decomposed into circular rotation and irregular motions using kinemetry. To quantify irregularities in the gas kinematics, we define three parameters: sigma_{PA} (standard deviation of the kinematic position angle), Delta phi (the average misalignment between kinematic and photometric position angles) and k_{3,5} (squared sum of the higher order Fourier terms). Using local, undistorted galaxies from SINGS, these can be used to establish the regularity of the gas velocity fields. Here we present the analysis of 22 distant galaxies in the MS0451.6-0305 field with 11 members at z=0.54. In this sample we find both field (4 out of 8) and cluster (3 out of 4) galaxies with velocity fields that are both irregular and asymmetric. We show that these fractions are underestimates of the actual number of galaxies with irregular velocity fields. The values of the (ir)regularity parameters for cluster galaxies are not very different from those of the field galaxies, implying that there are isolated field galaxies that are as distorted as the cluster members. None of the deviations in our small sample correlate with photometric/structural properties like luminosity or disk scale length in a significant way. Our 3D-spectroscopic method successfully maps the velocity field of distant galaxies, enabling the importance and efficiency of cluster specific interactions to be assessed quantitatively.

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arXiv2008

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 3.5m telescope at the Calar Alto observatory (CAHA). This instrument provides us with very stable flatfielding, a mandatory condition for reliably measuring intragroup diffuse light. The images were analyzed 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% of the total light of HCG 15, 35 and 51, respectively, is in the diffuse component, with colours that are compatible with old stellar populations and with mean surface brightness that can be as low as $28.4 {\rm B mag arcsec^{-2}}$. Dynamical masses, crossing times and mass to light ratios were recalculated using the new group parameters. Also tidal features were analyzed using the wavelet technique.

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arXiv2008

The galaxy populations from the centers to the infall regions in z~0.25 clusters

We conducted a panoramic spectroscopic campaign with MOSCA at the Calar Alto observatory. We acquired spectra of more than 500 objects. Approximately 150 of these spectra were of galaxies that are members of six different clusters, which differ in intrinsic X-ray luminosity. The wavelength range allows us to quantify the star formation activity by using the OII and the Halpha lines. This activity is examined in terms of the large-scale environment expressed by the clustercentric distance of the galaxies as well as on local scales given by the spatial galaxy densities. A global suppression of star-formation is detected in the outskirts of clusters, at about 3Rvir. Galaxies with ongoing star-formation have similar activity, regardless of the environment. Therefore, the decline of the star-formation activity inside the investigated clusters is driven mainly by the significant change in the fraction of active versus passive populations. This suggests that the suppression of the star-formation activity occurs on short timescales. We detect a significant population of red star-forming galaxies whose colors are consistent with the red-sequence of passive galaxies. They appear to be in an intermediate evolutionary stage between active and passive types. Since a suppression of star-formation activity is measured at large clustercentric distances and low projected densities, purely cluster-specific phenomena cannot fully explain the observed trends. Therefore, as suggested by other studies, group preprocessing may play an important role in transforming galaxies before they enter into the cluster environment. Since models predict that a significant fraction of galaxies observed in the outskirts may have already transversed through the cluster center, the effects of ram-pressure stripping cannot be neglected. (ABRIDGED)

astro-ph↗

arXiv2008

The effects of ram-pressure stripping on the internal kinematics of simulated spiral galaxies

We investigate the influence of ram-pressure stripping on the internal gas kinematics of simulated spiral galaxies. Additional emphasis is put on the question of how the resulting distortions of the gaseous disc are visible in the rotation curve and/or the full 2D velocity field of galaxies at different redshifts. A Milky-Way type disc galaxy is modelled in combined N-body/hydrodynamic simulations with prescriptions for cooling, star formation, stellar feedback, and galactic winds. This model galaxy moves through a constant density and temperature gas, which has parameters similar to the intra-cluster medium (ICM). Rotation curves (RCs) and 2D velocity fields of the gas are extracted from these simulations in a way that follows the procedure applied to observations of distant, small, and faint galaxies as closely as possible. We find that the appearance of distortions of the gaseous disc due to ram-pressure stripping depends on the direction of the acting ram pressure. In the case of face-on ram pressure, the distortions mainly appear in the outer parts of the galaxy in a very symmetric way. In contrast, in the case of edge-on ram pressure we find stronger distortions. The 2D velocity field also shows signatures of the interaction in the inner part of the disc. At angles smaller than 45 degrees between the ICM wind direction and the disc, the velocity field asymmetry increases significantly compared to larger angles. Compared to distortions caused by tidal interactions, the effects of ram-pressure stripping on the velocity field are relatively low in all cases and difficult to observe at intermediate redshift in seeing-limited observations. (abridged)

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