58 research outputs found
BUDHIES I: characterizing the environments in and around two clusters at z~0.2
We present the optical spectroscopy for the Blind Ultra Deep HI Environmental
Survey (BUDHIES). With the Westerbork Synthesis Radio Telescope, BUDHIES has
detected HI in over 150 galaxies in and around two Abell clusters at z~0.2.
With the aim of characterizing the environments of the HI-detected galaxies, we
obtained multi-fiber spectroscopy with the William Herschel Telescope. In this
paper, we describe the spectroscopic observations, report redshifts and EW[OII]
measurements for ~600 galaxies, and perform an environmental analysis. In
particular, we present cluster velocity dispersion measurements for 5 clusters
and groups in the BUDHIES volume, as well as a detailed substructure analysis.Comment: v2: Typos and small corrections after proofs added. 14 pages (plus
small appendix), 12 figures. Accepted for publication in MNRAS. Adobe Acrobat
Reader is required to correctly display the (3D) animated figures (Fig. 9).
Full data tables and supporting videos are also available at the BUDHIES
project website: http://www.astro.rug.nl/budhies
GASP. XII. The variety of physical processes occurring in a single galaxy group in formation
GAs Stripping Phenomena in galaxies with MUSE (GASP) is a program aimed at
studying gas removal processes in nearby galaxies in different environments. We
present the study of four galaxies that are part of the same group (z= 0.06359)
and highlight the multitude of mechanisms affecting the spatially resolved
properties of the group members. One galaxy is passive and shows a regular
stellar kinematics. The analysis of its star formation history indicates that
the quenching process lasted for a few Gyr and that the star formation declined
throughout the disk in a similar way, consistent with strangulation. Another
galaxy is characterised by a two-component stellar disk with an extended gas
disk that formed a few 10^8 yr ago, most likely as a consequence of gas
accretion. The third member is a spiral galaxy at the edges of the group, but
embedded in a filament. We hypothesise that the compression exerted by the
sparse intergalactic medium on the dense circumgalactic gas switches on star
formation in a number of clouds surrounding the galaxy ("cosmic web
enhancement"). Alternatively, also ram pressure stripping might be effective.
Finally, the fourth galaxy is a spiral with a truncated ionised gas disk and an
undisturbed stellar kinematics. An analytical model of the galaxy's restoring
pressure, and its location and velocity within the cluster, suggest ram
pressure is the most likely physical mechanism in action. This is the first
optical evidence for stripping in groups.Comment: 19 page, 12 figure
GASP XIII. Star formation in gas outside galaxies
Based on MUSE data from the GASP survey, we study the Halpha-emitting
extraplanar tails of 16 cluster galaxies at z~0.05 undergoing ram pressure
stripping. We demonstrate that the dominating ionization mechanism of this gas
(between 64% and 94% of the Halpha emission in the tails depending on the
diagnostic diagram used) is photoionization by young massive stars due to
ongoing star formation (SF) taking place in the stripped tails. This SF occurs
in dynamically quite cold HII clumps with a median Halpha velocity dispersion
sigma = 27 km s^-1. We study the characteristics of over 500 star-forming
clumps in the tails and find median values of Halpha luminosity L_{Halpha} = 4
X 10^38 erg s^-1, dust extinction A_V=0.5 mag, star formation rate SFR=0.003
M_sun yr^-1, ionized gas density n_e =52 cm^-3, ionized gas mass M_gas = 4 X
10^4 Msun, and stellar mass M_{*} = 3 X 10^6 Msun. The tail clumps follow
scaling relations (M_gas-M_{*}, L_{Halpha} -sigma, SFR-M_gas) similar to disk
clumps, and their stellar masses are comparable to Ultra Compact Dwarfs and
Globular Clusters.The diffuse gas component in the tails is ionized by a
combination of SF and composite/LINER-like emission likely due to thermal
conduction or turbulence. The stellar photoionization component of the diffuse
gas can be due either to leakage of ionizing photons from the HII clumps with
an average escape fraction of 18%, or lower luminosity HII regions that we
cannot individually identify.Comment: accepted for publication in MNRA
The colour-magnitude relation of elliptical and lenticular galaxies in the ESO Distant Cluster Survey
In this paper we study the colour-magnitude relation (CMR) for a sample of 172 morphologically classified elliptical and S0 cluster galaxies from the ESO Distant Cluster Survey (EDisCS) at 0.4 âČzâČ 0.8. The intrinsic colour scatter about the CMR is very small (ăÏintă= 0.076) in rest-frame UâV. However, there is a small minority of faint early-type galaxies (7 per cent) that are significantly bluer than the CMR. We observe no significant dependence of Ïint with redshift or cluster velocity dispersion. Because our sample is strictly morphologically selected, this implies that by the time cluster elliptical and S0 galaxies achieve their morphology, the vast majority have already joined the red sequence. The only exception seems to be the very small fraction of faint blue early types. Assuming that the intrinsic colour scatter is due to differences in stellar population ages, we estimate the galaxy formation redshift zF of each cluster and find that zF does not depend on the cluster velocity dispersion. However, zF increases weakly with cluster redshift within the EDisCS sample. This trend becomes very clear when higher redshift clusters from the literature are included. This suggests that, at any given redshift, in order to have a population of fully formed ellipticals and S0s they needed to have formed most of their stars â2-4 Gyr prior to observation. That does not mean that all early-type galaxies in all clusters formed at these high redshifts. It means that the ones we see already having early-type morphologies also have reasonably old stellar populations. This is partly a manifestation of the âprogenitor bias', but also a consequence of the fact that the vast majority of the early-type galaxies in clusters (in particular the massive galaxies) were already red (i.e. already had old stellar populations) by the time they achieved their morphology. Elliptical and S0 galaxies exhibit very similar colour scatter, implying similar stellar population ages. The scarcity of blue S0s indicates that, if they are the descendants of spirals whose star formation has ceased, the parent galaxies were already red when they became S0s. This suggests the red spirals found preferentially in dense environments could be the progenitors of these S0s. We also find that fainter early-type galaxies finished forming their stars later (i.e. have smaller zF), consistent with the cluster red sequence being built over time and the brightest galaxies reaching the red sequence earlier than fainter ones. Combining the CMR scatter analysis with the observed evolution in the CMR zero-point we find that the early-type cluster galaxy population must have had their star formation truncated/stopped over an extended period Îtâł 1 Gy
BUDHIES II:A phase-space view of H I gas stripping and star formation quenching in cluster galaxies
We investigate the effect of ram-pressure from the intracluster medium on the stripping of H I gas in galaxies in a massive, relaxed, X-ray bright, galaxy cluster at z = 0.2 from the Blind Ultra Deep H I Environmental Survey (BUDHIES). We use cosmological simulations, and velocity versus position phase-space diagrams to infer the orbital histories of the cluster galaxies. In particular, we embed a simple analytical description of ram-pressure stripping in the simulations to identify the regions in phase-space where galaxies are more likely to have been sufficiently stripped of their H I gas to fall below the detection limit of our survey. We find a striking agreement between the model predictions and the observed location of H I-detected and non-detected blue (late-type) galaxies in phase-space, strongly implying that ram-pressure plays a key role in the gas removal from galaxies, and that this can happen during their first infall into the cluster. However, we also find a significant number of gas-poor, red (early-type) galaxies in the infall region of the cluster that cannot easily be explained with our model of ram-pressure stripping alone. We discuss different possible additional mechanisms that could be at play, including the pre-processing of galaxies in their previous environment. Our results are strengthened by the distribution of galaxy colours (optical and UV) in phase-space, that suggests that after a (gas-rich) field galaxy falls into the cluster, it will lose its gas via ram-pressure stripping, and as it settles into the cluster, its star formation will decay until it is completely quenched. Finally, this work demonstrates the utility of phase-space diagrams to analyse the physical processes driving the evolution of cluster galaxies, in particular H I gas stripping
GASP IV: A muse view of extreme ram-pressure stripping in the plane of the sky: the case of jellyfish galaxy JO204
In the context of the GAs Stripping Phenomena in galaxies with Muse (GASP)
survey, we present the characterization of JO204, a jellyfish galaxy in A957, a
relatively low-mass cluster with . This galaxy
shows a tail of ionized gas that extends up to 30 kpc from the main body in the
opposite direction of the cluster center. No gas emission is detected in the
galaxy outer disk, suggesting that gas stripping is proceeding outside-in. The
stellar component is distributed as a regular disk galaxy; the stellar
kinematics shows a symmetric rotation curve with a maximum radial velocity of
200km/s out to 20 kpc from the galaxy center. The radial velocity of the gas
component in the central part of the disk follows the distribution of the
stellar component; the gas kinematics in the tail retains the rotation of the
galaxy disk, indicating that JO204 is moving at high speed in the intracluster
medium. Both the emission and radial velocity maps of the gas and stellar
components indicate ram-pressure as the most likely primary mechanism for gas
stripping, as expected given that JO204 is close to the cluster center and it
is likely at the first infall in the cluster. The spatially resolved star
formation history of JO204 provides evidence that the onset of ram-pressure
stripping occurred in the last 500 Myr, quenching the star formation activity
in the outer disk, where the gas has been already completely stripped. Our
conclusions are supported by a set of hydrodynamic simulations.Comment: accepted for publication in Ap
GASP XXVII: Gas-phase metallicity scaling relations in disk galaxies with and without ram-pressure stripping
Exploiting the data from the GAs Stripping Phenomena in galaxies with MUSE
(GASP) survey, we study the gas-phase metallicity scaling relations of a sample
of 29 cluster galaxies undergoing ram-pressure stripping and of a reference
sample of (16 cluster and 16 field) galaxies with no significant signs of gas
disturbance. We adopt the PYQZ code to infer the mean gas metallicity at the
effective radius and achieve a well-defined mass-metallicity relation (MZR) in
the stellar mass range with
a scatter of 0.12 dex. At any given mass, reference cluster and stripping
galaxies have similar metallicities, while the field galaxies with show on average lower gas metallicity than galaxies
in clusters. Our results indicate that at the effective radius the chemical
properties of the stripping galaxies are independent of the ram-pressure
stripping mechanism. Nonetheless, at the lowest masses we detect 4 stripping
galaxies well above the common MZR that suggest a more complex scenario.
Overall, we find signs of an anti-correlation between the metallicity and both
the star formation rate and the galaxy size, in agreement with previous
studies. No significant trends are instead found with the halo mass,
clustercentric distance and local galaxy density in clusters. In conclusion, we
advise a more detailed analysis of the spatially resolved gas metallicity maps
of the galaxies, able to highlight effects of gas redistribution inside the
disk due to the ram-pressure stripping.Comment: accepted for publication in ApJ, 24 pages, 21 figures, 2 table
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