arXiv subjects

Ananthan Karunakaran

Publications and source records attributed to Ananthan Karunakaran.

42 records · Page 3Linked to original sources

arXiv2019

Neutral Hydrogen Observations of Low Surface Brightness Galaxies around M101 and NGC 5485

We present atomic hydrogen (HI) observations using the Robert C. Byrd Green Bank Telescope along the lines-of-sight to 27 low surface brightness (LSB) dwarf galaxy candidates discovered in optical searches around M101. We detect HI reservoirs in 5 targets and place stringent upper limits on the remaining 22, implying that they are gas poor. The distances to our HI detections range from 7 Mpc --150 Mpc, demonstrating the utility of wide-bandpass HI observations as a follow-up tool. The systemic velocities of 3 detections are consistent with that of the NGC~5485 group behind M101, and we suggest that our 15 non-detections with lower distance limits from the optical are associated with and have been stripped by that group. We find that the gas richnesses of confirmed M101 satellites are broadly consistent with those of the Milky Way satellites, as well as with those of satellites around other hosts of comparable mass, when survey completeness is taken into account. This suggests that satellite quenching and gas stripping proceeds similarly around halos of similar mass, in line with theoretical expectations.

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arXiv2018

Systematically Measuring Ultra Diffuse Galaxies (SMUDGes). I. Survey Description and First Results in the Coma Galaxy Cluster and Environs

We present a homogeneous catalog of 275 large (effective radius $\gtrsim$ 5.3 arcsec) ultra-diffuse galaxy (UDG) candidates lying within an $\approx$ 290 square degree region surrounding the Coma cluster. The catalog results from our automated postprocessing of data from the Legacy Surveys, a three-band imaging survey covering 14,000 square degrees of the extragalactic sky. We describe a pipeline that identifies UDGs and provides their basic parameters. The survey is as complete in these large UDGs as previously published UDG surveys of the central region of the Coma cluster. We conclude that the majority of our detections are at roughly the distance of the Coma cluster, implying effective radii $\ge 2.5$ kpc, and that our sample contains a significant number of analogs of DF 44, where the effective radius exceeds 4 kpc, both within the cluster and in the surrounding field. The $g-z$ color of our UDGs spans a large range, suggesting that even large UDGs may reflect a range of formation histories. A majority of the UDGs are consistent with being lower stellar mass analogs of red sequence galaxies, but we find both red and blue UDG candidates in the vicinity of the Coma cluster and a relative overabundance of blue UDG candidates in the lower density environments and the field. Our eventual processing of the full Legacy Surveys data will produce the largest, most homogeneous sample of large UDGs.

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arXiv2018

Evidence for Ultra-Diffuse Galaxy `Formation' Through Galaxy Interactions

We report the discovery of two ultra-diffuse galaxies (UDGs) which show clear evidence for association with tidal material and interaction with a larger galaxy halo, found during a search of the Wide portion of the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). The two new UDGs, NGC2708-Dw1 and NGC5631-Dw1, are faint ($M_g$=$-$13.7 and $-$11.8 mag), extended ($r_h$=2.60 and 2.15 kpc) and have low central surface brightness ($μ(g,0)$=24.9 and 27.3 mag arcsec$^{-2}$), while the stellar stream associated with each has a surface brightness $μ(g)$$\gtrsim$28.2 mag arcsec$^{-2}$. These observations provide evidence that the origin of some UDGs may connect to galaxy interactions, either by transforming normal dwarf galaxies by expanding them, or because UDGs can collapse out of tidal material (i.e. they are tidal dwarf galaxies). Further work is needed to understand the fraction of the UDG population `formed' through galaxy interactions, and wide field searches for diffuse dwarf galaxies will provide further clues to the origin of these enigmatic stellar systems.

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arXiv2018

Atomic Gas in Blue Ultra Diffuse Galaxies around Hickson Compact Groups

We have found the atomic gas (HI) reservoirs of the blue ultra diffuse galaxy (UDG) candidates identified by Róman and Trujillo in images near Hickson Compact Groups (HCGs). We confirm that all of the objects are indeed UDGs with effective radii R_e > 1.5 kpc. Three of them are likely to be gravitationally bound to the HCG near which they project, one is plausibly gravitationally bound to the nearest HCG, and one is in the background. We measure HI masses and velocity widths for each object directly from the spectra, and use the widths together with the UDG effective radii to estimate dynamical masses and halo spin parameters. The location of the blue UDGs in the HI mass - stellar mass plane is consistent with that of the broader gas-rich galaxy population, and both their HI masses and gas richnesses are correlated with their effective radii. The blue UDGs appear to be low-mass objects with high-spin halos, although their properties are not as extreme as those of the faintest diffuse objects found in HI searches. The data presented here highlight the potential of single-dish radio observations for measuring the physical properties of blue diffuse objects detected in the optical.

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arXiv2016

First results from the MADCASH Survey: A Faint Dwarf Galaxy Companion to the Low Mass Spiral Galaxy NGC 2403 at 3.2 Mpc

We report the discovery of the faintest known dwarf galaxy satellite of an LMC stellar-mass host beyond the Local Group, based on deep imaging with Subaru/Hyper Suprime-Cam. MADCASH J074238+652501-dw lies $\sim$35 kpc in projection from NGC 2403, a dwarf spiral galaxy at $D$$\approx$3.2 Mpc. This new dwarf has $M_{g} = -7.4\pm0.4$ and a half-light radius of $168\pm70$ pc, at the calculated distance of $3.39\pm0.41$ Mpc. The color-magnitude diagram reveals no evidence of young stellar populations, suggesting that MADCASH J074238+652501-dw is an old, metal-poor dwarf similar to low luminosity dwarfs in the Local Group. The lack of either detected HI gas ($M_{\rm HI}/L_{V} < 0.69 M_\odot/L_\odot$, based on Green Bank Telescope observations) or $GALEX$ NUV/FUV flux enhancement is consistent with a lack of young stars. This is the first result from the MADCASH (Magellanic Analog Dwarf Companions And Stellar Halos) survey, which is conducting a census of the stellar substructure and faint satellites in the halos of Local Volume LMC analogs via resolved stellar populations. Models predict a total of $\sim$4-10 satellites at least as massive as MADCASH J074238+652501-dw around a host with the mass of NGC 2403, with 2-3 within our field of view, slightly more than the one such satellite observed in our footprint.

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arXiv2015

Comparing galaxy disk and star-formation properties in X-ray bright and faint groups and clusters

Galaxy morphologies and star-formation rates depend on environment. Galaxies in under-dense regions are generally star-forming and disky whereas galaxies in overdense regions tend to be early-type and not actively forming stars. The mechanism(s) responsible for star-formation quenching and morphological transformation remain unclear, although many processes have been proposed. We study the dependence of star-formation and morphology on X-ray luminosity for galaxies in Sloan Digital Sky Survey Data Release 7 (SDSS-DR7) groups and clusters. While controlling for stellar and halo mass dependencies, we find that galaxies in X-ray strong groups and clusters have preferentially low star-forming and disk fractions -- with the differences being strongest at low stellar masses. The trends that we observe do not change when considering only galaxies found within or outside of the X-ray radius of the host group. When considering central and satellite galaxies separately we find that this dependence on X-ray luminosity is only present for satellites, and we show that our results are consistent with "galaxy stangulation" as a mechanism for quenching these satellites. We investigate the dynamics of the groups and clusters in the sample, and find that the velocity distributions of galaxies beyond the virial radius in low X-ray luminosity halos tend to be less Gaussian in nature than the rest of the data set. This may be indicative of low X-ray luminosity groups and clusters having enhanced populations of star-forming and disk galaxies as a result of recent accretion.

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