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Register a new userThe detection of ultra-faint low surface brightness dwarf galaxies in the Virgo Cluster: a Probe of Dark Matter and Baryonic Physics
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We have discovered 11 ultra-faint ($rlesssim 22.1$) low surface brightness (LSB, central surface brightness $23lesssim mu_rlesssim 26$) dwarf galaxy candidates in one deep Virgo field of just $576$ arcmin$^2$ obtained by the Large Binocular Camera (LBC) at the Large Binocular Telescope (LBT). Their association with the Virgo cluster is supported by their distinct position in the central surface brightness - total magnitude plane with respect to the background galaxies of similar total magnitude. They have typical absolute magnitudes and scale sizes, if at the distance of Virgo, in the range $-13lesssim M_rlesssim -9$ and $250lesssim r_slesssim 850$ pc, respectively. Their colors are consistent with a gradually declining star formation history with a specific star formation rate of the order of $10^{-11}$ yr$^{-1}$, i.e. 10 times lower than that of main sequence star forming galaxies. They are older than the cluster formation age and appear regular in morphology. They represent the faintest extremes of the population of low luminosity LSB dwarfs that has been recently detected in wider surveys of the Virgo cluster. Thanks to the depth of our observations we are able to extend the Virgo luminosity function down to $M_rsim -9.3$ (corresponding to total masses $Msim 10^7$ M$_{odot}$), finding an average faint-end slope $alphasimeq -1.4$. This relatively steep slope puts interesting constraints on the nature of the Dark Matter and in particular on warm Dark Matter (WDM) often invoked to solve the overprediction of the dwarf number density by the standard CDM scenario. We derive a lower limit on the WDM particle mass $>1.5$ keV.
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We report the automatic detection of a new sample of very low surface brightness (LSB) galaxies, likely members of the Virgo cluster. We introduce our new software, {tt DeepScan}, that has been designed specifically to detect extended LSB features automatically using the DBSCAN algorithm. We demonstrate the technique by applying it over a 5 degree$^2$ portion of the Next-Generation Virgo Survey (NGVS) data to reveal 53 low surface brightness galaxies that are candidate cluster members based on their sizes and colours. 30 of these sources are new detections despite the region being searched specifically for LSB galaxies previously. Our final sample contains galaxies with $26.0leqlangle mu_{e}rangleleq28.5$ and $19leq m_{g}leq21$, making them some of the faintest known in Virgo. The majority of them have colours consistent with the red sequence, and have a mean stellar mass of $10^{6.3pm0.5} M_{odot}$ assuming cluster membership. After using {tt ProFit} to fit Sersic profiles to our detections, none of the new sources have effective radii larger than 1.5 Kpc and do not meet the criteria for ultra-diffuse galaxy (UDG) classification, so we classify them as ultra-faint dwarfs.
The observed rotation curves of low surface brightness (LSB) galaxies play an essential role in studying dark matter, and indicate that there exists a central constant density dark matter core. However, the cosmological N-body simulations of cold dark matter predict an inner cusped halo with a power-law mass density distribution, and cant reproduce a central constant-density core. This phenomenon is called cusp-core problem. When dark matter is quiescent and satisfies the condition for hydrostatic equilibrium, using the equation of state can get the density profile in the static and spherically symmetric space-time. To solve the cusp-core problem, we assume that the equation of state is independent of the scaling transformation. Its lower order approximation for this type of equation of state can naturally lead to a special case, i.e. $p=zetarho+2epsilon V_{rot}^{2}rho$, where $p$ and $rho$ are the pressure and density, $V_{rot}$ is the rotation velocity of galaxy, $zeta$ and $ epsilon$ are positive constants. It can obtain a density profile that is similar to the pseudo-isothermal halo model when $epsilon$ is around $0.15$. To get a more widely used model, let the equation of state include the polytropic model, i.e. $p= frac{zeta}{rho_{0}^{s}}rho^{1+s}+ 2epsilon V_{rot}^{2}rho$, we can get other kinds of density profiles, such as the profile that is nearly same with the Burkert profile, where $s$ and $rho_{0}$ are positive constants.
We describe a new, deep photographic survey of the Virgo Cluster which uses multiple exposures on Tech Pan film with the United Kingdom Schmidt Telescope to probe the dwarf population to fainter surface brightness limits than previous surveys. We have identified galaxies having sizes (>= 3 arcsec scale length) and surface brightnesses (<= 24.5 R mag arcsec^-2) characteristic of those expected for dwarf spheroidal galaxies in the cluster. The survey is providing substantial samples of extremely low luminosity galaxies outside the environment of the Local Group and nearby groups for the first time. An initial study of two small areas has found dwarf spheroidal candidates in large numbers (500 deg^-2) which indicate a steep, continuously rising luminosity function at low luminosities.
Recent advancements in the imaging of low-surface-brightness objects revealed numerous ultra-diffuse galaxies in the local Universe. These peculiar objects are unusually extended and faint: their effective radii are comparable to the Milky Way, but their surface brightnesses are lower than that of dwarf galaxies. Their ambiguous properties motivate two potential formation scenarios: the failed Milky Way and the dwarf galaxy scenario. In this paper, for the first time, we employ X-ray observations to test these formation scenarios on a sample of isolated, low-surface-brightness galaxies. Since hot gas X-ray luminosities correlate with the dark matter halo mass, failed Milky Way-type galaxies, which reside in massive dark matter halos, are expected to have significantly higher X-ray luminosities than dwarf galaxies, which reside in low-mass dark matter halos. We perform X-ray photometry on a subset of low-surface-brightness galaxies identified in the Hyper Suprime-Cam Subaru survey, utilizing the XMM-Newton XXL North survey. We find that none of the individual galaxies show significant X-ray emission. By co-adding the signal of individual galaxies, the stacked galaxies remain undetected and we set an X-ray luminosity upper limit of ${L_{rm{0.3-1.2keV}}leq6.2 times 10^{37} (d/65 rm{Mpc})^2 rm{erg s^{-1}}}$ for an average isolated low-surface-brightness galaxy. This upper limit is about 40 times lower than that expected in a galaxy with a massive dark matter halo, implying that the majority of isolated low-surface-brightness galaxies reside in dwarf-size dark matter halos.
We present Keck/DEIMOS spectroscopy of globular clusters (GCs) around the ultra-diffuse galaxies (UDGs) VLSB-B, VLSB-D, and VCC615 located in the central regions of the Virgo cluster. We spectroscopically identify 4, 12, and 7 GC satellites of these UDGs, respectively. We find that the three UDGs have systemic velocities ($V_{sys}$) consistent with being in the Virgo cluster, and that they span a wide range of velocity dispersions, from $sim 16$ to $sim 47$ km/s, and high dynamical mass-to-light ratios within the radius that contains half the number of GCs ($ 407^{+916}_{-407}$, $21^{+15}_{-11}$, $60^{+65}_{-38}$, respectively). VLSB-D shows possible evidence for rotation along the stellar major axis and its $V_{sys}$ is consistent with that of the massive galaxy M84 and the center of the Virgo cluster itself. These findings, in addition to having a dynamically and spatially ($sim 1$ kpc) off-centered nucleus and being extremely elongated, suggest that VLSB-D could be tidally perturbed. On the contrary, VLSB-B and VCC615 show no signals of tidal deformation. Whereas the dynamics of VLSB-D suggest that it has a less massive dark matter halo than expected for its stellar mass, VLSB-B and VCC615 are consistent with a $sim 10^{12}$ M$_{odot}$ dark matter halo. Although our samples of galaxies and GCs are small, these results suggest that UDGs may be a diverse population, with their low surface brightnesses being the result of very early formation, tidal disruption, or a combination of the two.
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