Dashing through the cluster: An X-ray to radio view of UGC 10420 undergoing ram-pressure stripping

We present multi-wavelength data and analysis, including new FUV AstroSat/UVIT observations of the spiral galaxy UGC 10420 (z=0.032), a member of the cluster Abell 2199. UGC 10420 is present on the edge of the X-ray emitting region of the cluster at a distance of ~ 680 kpc from the centre. The FUV data shows intense knots of star formation on the leading edge of the galaxy, accompanied by a tail of the same on the diametrically opposite side. Our analysis shows that the images of the galaxy disk in the optical and mid-infrared are much smaller in size than that in the FUV. While the broadband optical colours of UGC 10420 are typical of a post-starburst galaxy, the SFR derived from a UV-to-IR spectral energy distribution is at least a factor of nine higher than that expected for a star-forming field galaxy of similar mass at its redshift. A careful removal of the contribution of the diffuse intracluster gas shows that the significant diffuse X-ray emission associated with the inter-stellar medium of UGC 10420 has a temperature, T_X = 0.24^{+0.09}_{-0.06} keV (0.4-2.0 keV) and luminosity, L_X = 1.8+/-0.9 x 10^{40} erg/s, which are typical of the X-ray emission from late-type spiral galaxies. Our analysis favours a scenario where the interaction of a galaxy with the hot intra-cluster medium of the cluster, perturbs the gas in the galaxy causing starburst in the leading edge of the disk. On the other hand, the turbulence thus developed may also push some of the gas out of the disk. Interactions between the gas ejected from the galaxy and the intracluster medium can then locally trigger star formation in the wake of the galaxy experiencing ram-pressure stripping. Our data however does not rule out the possibility of a flyby encounter with a neighbouring galaxy, although no relevant candidates are observed in the vicinity of UGC 10420. (abridged)Comment: Accepted for publication in the Publication of the Astronomical Society of Australia (PASA). 16 pages, 11 figure

The evolution of dwarf galaxies in the Coma supercluster

We employ spectroscopic and photometric data from SDSS DR7, in a 500 sq degree region, to understand the evolution of dwarf (~M*+2<M_z<M*+4) galaxies in the Coma supercluster (z=0.023). We show that in the Coma supercluster, the red dwarfs are mostly concentrated in the dense cores of the Coma and Abell 1367 clusters, and in the galaxy groups embedded in the filament connecting them. The post-starburst (k+A) dwarfs however are found in the infall regions of the Coma and Abell 1367 clusters, and occasionally in galaxy groups embedded along the filament, suggesting that strong velocity fields prevalent in the vicinity of deep potential wells may be closely related to the mechanism(s) leading to the post-starburst phase in dwarf galaxies. Moreover, the blue colour of some k+A dwarfs in the Coma cluster, found within its virial radius, suggests that the star formation in these galaxies was quenched very rapidly in the last 500 Myr. More than 60% of all red dwarf galaxies in the supercluster have 0-3 ang of H_\delta in absorption, which suggests that a major episode of star formation occurred in a non-negligible fraction of these galaxies, ending within the last Gyr, allowing them to move to the red sequence. The distribution of the blue dwarf galaxies in the Coma supercluster is bimodal in the EW(H_\alpha)-EW(H_\delta) plane, with one population having very high emission in H_\alpha, and some emission in H_\delta. A sub-population of blue dwarfs is coincident with the red dwarfs in the EW(H_\alpha)-EW(H_\delta) plane, showing absorption in H_\delta and relatively lower emission in H_\alpha. We suggest that a large fraction of the latter population are the progenitors of the passive dwarf galaxies that are abundantly found in the cores of low-redshift rich clusters such as Coma.Comment: 6 Pages, 5 Figures, Accepted for publication in MNRA

Evidence for galaxies being pre-processed before accreted into clusters

I use the spectroscopic data for galaxies in and around 28 nearby (0.02 ≤ z ≤ 0.06) X-ray bright galaxy clusters, to show that the incidence of k+A (or post-starburst) galaxies (EW(Ha) 3Å in absorption) may be correlated with the accretion of small galaxy groups in clusters. At r < 2r200, the k+A galaxies are found in regions of higher galaxy density relative to other cluster galaxies. The k+A galaxies have a positively skewed distribution of absolute velocity, v/σv, where vlos is the difference between the line-of-sight velocity of the galaxy and the cluster's mean, and σv is the cluster's velocity dispersion. This distribution is statistically different from that of other cluster galaxies within 2r200, and in the same absolute velocity range. Moreover, 87 per cent of clusters in the sample studied here show statistically significant substructure in their velocity distribution, and 91.4 per cent of all the k+A galaxies are found to be a part of one of these substructures with 4-10 members. These results suggest that star formation in these k+A galaxies is likely to have been quenched due to 'pre-processing' in a poor group-like environment before they are accreted into clusters. I also find a mild, but statistically significant trend in the fraction of k+A galaxies increasing with the temperature of the X-ray emitting gas in clusters

The Star Formation Reference Survey - III. A multiwavelength view of star formation in nearby galaxies

We present multiwavelength global star formation rate (SFR) estimates for 326 galaxies from the Star Formation Reference Survey in order to determine the mutual scatter and range of validity of different indicators. The widely used empirical SFR recipes based on 1.4 GHz continuum, 8.0 μm polycyclic aromatic hydrocarbons (PAHs), and a combination of far-infrared (FIR) plus ultraviolet (UV) emission are mutually consistent with scatter of ≲0.3 dex. The scatter is even smaller, ≲0.24 dex, in the intermediate luminosity range 9.3 \u3c log(L60 μm/L⊙) \u3c 10.7. The data prefer a non-linear relation between 1.4 GHz luminosity and other SFR measures. PAH luminosity underestimates SFR for galaxies with strong UV emission. A bolometric extinction correction to far-UV luminosity yields SFR within 0.2 dex of the total SFR estimate, but extinction corrections based on UV spectral slope or nuclear Balmer decrement give SFRs that may differ from the total SFR by up to 2 dex. However, for the minority of galaxies with UV luminosity \u3e 5 × 109 L⊙ or with implied far-UV extinction \u3c 1mag, the UV spectral slope gives extinction corrections with 0.22 dex uncertainty

The velocity modulation of galaxy properties in and near clusters: quantifying the decrease in star formation in backsplash galaxies

The efficiency of recent star formation (SF) in galaxies increases with increasing projected distance from the centre of a cluster out to several times its virial radius (R_v). Using a complete sample of galaxies in 268 clusters from the SDSS DR4, we investigate how, at a given projected radius from the cluster centre, M* and SF properties of a galaxy depend on its absolute line-of-sight velocity in the cluster rest frame, |v_LOS|. We find that for R<0.5 R_v, the fraction of high mass non-BCG galaxies increases towards the centre for low |v_LOS|. At a given projected radius, the fraction of Galaxies with Ongoing or Recent (<1-3 Gyr) Efficient Star Formation (GORES, with EW(H_delta)>2 ang & D_4000>1.5) is slightly but significantly lower for low |v_LOS| galaxies than for their high velocity counterparts. We study these observational trends with the help of a dark matter (DM) cosmological simulation. We find that the backsplash particles account for at least one-third (half) of all particles at projected radii slightly greater than the virial radius and |v_LOS|<sigma_v. The deprojection of the GORES fraction leads to a saturated linear increase with radius. We fit simple models of the fraction of GORES as a function of class only or class and distance to the cluster centre (as in our deprojected fraction). In our best-fitting model GORES account for 13% of galaxies within the virial sphere, 11% of the virial population, 34% of the distant (for projected radii R<2 R_v) infall population and 19% of the backsplash galaxies. Given the 1-3 Gyr lookback time of our GORES indicators, these results suggest that SF in a galaxy is almost completely quenched in a single passage through the cluster.Comment: 22 pages, 17 figures, MNRAS, 416, 2882, Labels for Figure 14 revise

Galaxy And Mass Assembly (GAMA): blue spheroids within 87 Mpc

© 2017 The Author(s). In this paper, we test if nearby blue spheroid (BSph) galaxies may become the progenitors of star-forming spiral galaxies or passively evolving elliptical galaxies. Our sample comprises 428 galaxies of various morphologies in the redshift range 0.002 < Ζ < 0.02 (8-87 Mpc) with panchromatic data from the Galaxy and Mass Assembly survey. We find that BSph galaxies are structurally (mean effective surface brightness, effective radius) very similar to their passively evolving red counterparts. However, their star formation and other properties such as colour, age, and metallicity are more like star-forming spirals than spheroids (ellipticals and lenticulars). We show that BSph galaxies are statistically distinguishable from other spheroids as well as spirals in the multidimensional space mapped by luminosity-weighted age, metallicity, dust mass, and specific star formation rate. We use HI data to reveal that some of the BSphs are (further) developing their discs, hence their blue colours. They may eventually become spiral galaxies - if sufficient gas accretion occurs - or more likely fade into low-mass red galaxies

Galaxy And Mass Assembly (GAMA): properties and evolution of red spiral galaxies

For abstract see article

THE SAMI GALAXY SURVEY: GALAXY INTERACTIONS and KINEMATIC ANOMALIES IN ABELL 119

Galaxy mergers are important events that can determine the fate of a galaxy by changing its morphology, star formation activity and mass growth. Merger systems have commonly been identified from their disturbed morphologies, and we now can employ integral field spectroscopy to detect and analyze the impact of mergers on stellar kinematics as well. We visually classified galaxy morphology using deep images (μr = 28 mag arcsec- 2 ) taken by the Blanco 4 m telescope at the Cerro Tololo Inter-American Observatory. In this paper we investigate 63 bright (Mr >-19.3) spectroscopically selected galaxies in Abell 119, of which 53 are early type and 20 show a disturbed morphology by visual inspection. A misalignment between the major axes in the photometric image and the kinematic map is conspicuous in morphologically disturbed galaxies. Our sample is dominated by early-type galaxies, yet it shows a surprisingly tight TullyFisher relation except for the morphologically disturbed galaxies which show large deviations. Three out of the eight slow rotators in our sample are morphologically disturbed. The morphologically disturbed galaxies are generally more asymmetric, visually as well as kinematically. Our findings suggest that galaxy interactions, including mergers and perhaps fly-bys, play an important role in determining the orientation and magnitude of a galaxys angular momentum