An official website of the United States government
Abstract The radio galaxy M87 is the central dominant galaxy of the Virgo Cluster. Very high-energy (VHE, ≳0.1 TeV) emission from M87 has been detected by imaging air Cherenkov telescopes. Recently, marginal evidence for VHE long-term emission has also been observed by the High Altitude Water Cherenkov Observatory, a gamma-ray and cosmic-ray detector array located in Puebla, Mexico. The mechanism that produces VHE emission in M87 remains unclear. This emission originates in its prominent jet, which has been spatially resolved from radio to X-rays. In this paper, we construct a spectral energy distribution from radio to gamma rays that is representative of the nonflaring activity of the source, and in order to explain the observed emission, we fit it with a lepto-hadronic emission model. We found that this model is able to explain nonflaring VHE emission of M87 as well as an orphan flare reported in 2005.
more »
« less
HaloSat Observation of the Virgo Intracluster Medium
Abstract Contained within a galaxy cluster, the Intracluster Medium is comprised of hot, X-ray emitting material between member galaxies. The nearest (∼16.1 Mpc) large galaxy cluster is Virgo. Virgo covers an approximately 12° diameter field, making it challenging to observe in its entirety. The HaloSat satellite utilized a 7° radius field of view to obtain the first full cluster observations since 1994. We then fit the cluster spectra with a plasma emission model of fixed metallicity. Our best fit temperature is kT = 1.39 ± 0.11 keV. We report a cluster luminosity of 5.8 ± 0.7 × 10 43 erg s −1 and an emission measure of 5.8 ± 0.6 × 10 66 cm −3 .
more »
« less
- Award ID(s):
- 2012916
- PAR ID:
- 10330838
- Date Published:
- Journal Name:
- Research Notes of the AAS
- Volume:
- 5
- Issue:
- 8
- ISSN:
- 2515-5172
- Page Range / eLocation ID:
- 185
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract We use deep Hubble Space Telescope imaging to derive a distance to the Virgo Cluster ultradiffuse galaxy (UDG) VCC 615 using the tip of the red giant branch (TRGB) distance estimator. We detect 5023 stars within the galaxy, down to a 50% completeness limit of F814W ≈ 28.0, using counts in the surrounding field to correct for contamination due to background sources and Virgo intracluster stars. We derive an extinction-corrected F814W tip magnitude of m tip , 0 = 27.19 − 0.05 + 0.07 , yielding a distance of d = 17.7 − 0.4 + 0.6 Mpc. This places VCC 615 on the far side of the Virgo Cluster ( d Virgo = 16.5 Mpc), at a Virgocentric distance of 1.3 Mpc and near the virial radius of the main body of Virgo. Coupling this distance with the galaxy’s observed radial velocity, we find that VCC 615 is on an outbound trajectory, having survived a recent passage through the inner parts of the cluster. Indeed, our orbit modeling gives a 50% chance the galaxy passed inside the Virgo core ( r < 620 kpc) within the past gigayear, although very close passages directly through the cluster center ( r < 200 kpc) are unlikely. Given VCC 615's undisturbed morphology, we argue that the galaxy has experienced no recent and sudden transformation into a UDG due to the cluster potential, but rather is a long-lived UDG whose relatively wide orbit and large dynamical mass protect it from stripping and destruction by the Virgo cluster tides. Finally, we also describe the serendipitous discovery of a nearby Virgo dwarf galaxy projected 90″ (7.2 kpc) away from VCC 615.more » « less
-
ABSTRACT We use high-resolution Hubble Space Telescope imaging data of dwarf galaxies in the Local Volume ($$\lesssim {11}\, \mathrm{Mpc}$$) to parameterize 19 newly discovered nuclear star clusters (NSCs). Most of the clusters have stellar masses of $$M_{\star }^{\mathrm{nsc}} \lesssim 10^{6}{\, {\rm M}_{\odot }}$$ and compare to Galactic globular clusters in terms of ellipticity, effective radius, stellar mass, and surface density. The clusters are modelled with a Sérsic profile and their surface brightness evaluated at the effective radius reveals a tight positive correlation to the host galaxy stellar mass. Our data also indicate an increase in slope of the density profiles with increasing mass, perhaps indicating an increasing role for in situ star formation in more massive hosts. We evaluate the scaling relation between the clusters and their host galaxy stellar mass to find an environmental dependence: for NSCs in field galaxies, the slope of the relation is $$\alpha = 0.82^{+0.08}_{-0.08}$$ whereas $$\alpha = 0.55^{+0.06}_{-0.05}$$ for dwarfs in the core of the Virgo cluster. Restricting the fit for the cluster to $$M_{\star }^{\mathrm{gal}} \ge 10^{6.5}{\, {\rm M}_{\odot }}$$ yields $$\alpha = 0.70^{+0.08}_{-0.07}$$, in agreement with the field environment within the 1σ interval. The environmental dependence is due to the lowest-mass nucleated galaxies and we speculate that this is either due to an increased number of progenitor globular clusters merging to become an NSC, or due to the formation of more massive globular clusters in dense environments, depending on the initial globular cluster mass function. Our results clearly corroborate recent results in that there exists a tight connection between NSCs and globular clusters in dwarf galaxies.more » « less
-
We use deep Hubble Space Telescope imaging to study the evolutionary state of of the Virgo Cluster ultradiffuse galaxy (UDG) VCC 615. Using the tip of the red giant branch method, we pinpoint the galaxy's location with Virgo to be on the far side of the cluster, near the Virgo virial radius. When combined with the galaxy's measured line of sight velocity, we find the galaxy to be on an outbound orbit, having likely passed near the cluster core within the past billion years. Given the galaxy's largely undisturbed morphology, we argue that the galaxy has experienced no recent and sudden transformation into a UDG due to the cluster potential, but rather is a long-lived UDG whose relatively wide orbit and large dynamical mass protect it from stripping and destruction by Virgo cluster tides. Our Hubble imaging resolves individual globular clusters within VCC 615 down to a limiting half-light radius of 1 pc, allowing for a clean determination of the size distribution and luminosity function of the galaxy's globular cluster population. The total mass of the galaxy derived from the size of its globular cluster population is comparable to our previous work estimate from the mass from the globular cluster kinematics. Finally, we also derive the structural properties of the galaxy's nucleus and find them similar to the properties of ultracompact galaxies (UCDs) in the Virgo core, suggesting a dynamical link between UCDs and nucleated UDGs in cluster environments.more » « less
-
It is now well established that galaxies have different morphologies, gas contents, and star formation rates (SFR) in dense environments like galaxy clusters. The impact of environmental density extends to several virial radii, and galaxies appear to be pre-processed in filaments and groups before falling into the cluster. Our goal is to quantify this pre-processing in terms of gas content and SFR, as a function of density in cosmic filaments. We have observed the two first CO transitions in 163 galaxies with the IRAM-30 m telescope, and added 82 more measurements from the literature, thus forming a sample of 245 galaxies in the filaments around the Virgo cluster. We gathered HI-21cm measurements from the literature and observed 69 galaxies with the Nançay telescope to complete our sample. We compare our filament galaxies with comparable samples from the Virgo cluster and with the isolated galaxies of the AMIGA sample. We find a clear progression from field galaxies to filament and cluster galaxies for decreasing SFR, increasing fraction of galaxies in the quenching phase, an increasing proportion of early-type galaxies, and decreasing gas content. Galaxies in the quenching phase, defined as having a SFR below one-third of that of the main sequence (MS), are only between 0% and 20% in the isolated sample, according to local galaxy density, while they are 20%–60% in the filaments and 30%–80% in the Virgo cluster. Processes that lead to star formation quenching are already at play in filaments; they depend mostly on the local galaxy density, while the distance to the filament spine is a secondary parameter. While the HI-to-stellar-mass ratio decreases with local density by an order of magnitude in the filaments, and two orders of magnitude in the Virgo cluster with respect to the field, the decrease is much less for the H 2 -to-stellar-mass ratio. As the environmental density increases, the gas depletion time decreases, because the gas content decreases faster than the SFR. This suggests that gas depletion precedes star formation quenching.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3847/2515-5172/ac1ad5
