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Register a new userThe Spectral and Temporal Properties of Transient Sources in Early-Type Galaxies
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We report the spectral and temporal variability properties of 18 candidate transient and potential transient (TC and PTC) sources detected in deep multi-epoch Chandra observation of the nearby elliptical galaxies, NGC 3379, NGC 4278 and NGC 4697. Only one source can be identified with a background counterpart, leaving 17 TCs + PTCs in the galaxies. Of these, 14 are in the galaxy field, supporting the theoretical picture that the majority of field X-ray binaries (XRBs) will exhibit transient accretion for >75% of their lifetime. Three sources are coincident with globular clusters (GCs), including two high-luminosity candidate black hole (BH) XRBs, with Lx=5.4E38 erg/s, and Lx=2.8E39 erg/s, respectively. The spectra, luminosities and temporal behavior of these 17 sources suggest that the transient population is heterogeneous, including neutron star (NS) and BH XRBs in both normal and high-rate accretion modes, and super soft sources containing white dwarf binaries. Our TC and PTC detections are noticeably fewer that the number expected from the populations synthesis (PS) models of Fragos et al. (2009), tailored to our new Chandra pointings of NGC 4278. We attribute this discrepancy to the PS assumption that the transient population is composed of NS XRBs, as well as differences between the statistical analysis and error estimates used in the model and our observations.
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We present very early UV to optical photometric and spectroscopic observations of the peculiar Type IIn supernova (SN) 2011ht in UGC 5460. The UV observations of the rise to peak are only the second ever recorded for a Type IIn SN and are by far the most complete. The SN, first classified as a SN impostor, slowly rose to a peak of M_V sim -17 in sim55 days. In contrast to the sim2 magnitude increase in the v-band light curve from the first observation until peak, the UV flux increased by >7 magnitudes. The optical spectra are dominated by strong, Balmer emission with narrow peaks (FWHMsim600 km/s), very broad asymmetric wings (FWHMsim4200 km/s), and blue shifted absorption (sim300 km/s) superposed on a strong blue continuum. The UV spectra are dominated by FeII, MgII, SiII, and SiIII absorption lines broadened by sim1500 km/s. Merged X-ray observations reveal a L_(0.2-10)=(1.0+/-0.2)x10^(39) erg/s. Some properties of SN 2011ht are similar to SN impostors, while others are comparable to Type IIn SNe. Early spectra showed features typical of luminous blue variables at maximum and during giant eruptions. However, the broad emission profiles coupled with the strong UV flux have not been observed in previous SN impostors. The absolute magnitude and energetics (~2.5x10^(49) ergs in the first 112 days) are reminiscent of normal Type IIn SN, but the spectra are of a dense wind. We suggest that the mechanism for creating this unusual profile could be a shock interacting with a shell of material that was ejected a year before the discovery of the SN.
Accretion onto central massive black holes in galaxies is often modelled with the Bondi solution. In this paper we study a generalization of the classical Bondi accretion theory, considering the additional effects of the gravitational potential of the host galaxy, and of electron scattering in the optically thin limit. We provide a general analysis of the bias in the estimates of the Bondi radius and mass accretion rate, when adopting as fiducial values for the density and temperature at infinity the values of these quantities measured at finite distance from the central black hole. We also give general formulae to compute the correction terms of the critical accretion parameter in relevant asymptotic regimes. A full analytical discussion is presented in the case of an Hernquist galaxy, when the problem reduces to the discussion of a cubic equation, therefore allowing for more than one critical point in the accretion structure. The results are useful for observational works (especially in the case of low-luminosity systems), as well as for numerical simulations, where accretion rates are usually defined in terms of the gas properties near the
What happens to dwarf galaxies as they enter the cluster potential well is one of the main unknowns in studies of galaxy evolution. Several evidence suggests that late-type galaxies enter the cluster and are transformed to dwarf early-type galaxies (dEs). We study the Virgo cluster to understand which mechanisms are involved in this transformation. We find that the dEs in the outer parts of Virgo have rotation curves with shapes and amplitudes similar to late-type galaxies of the same luminosity. These dEs are rotationally supported, have disky isophotes, and younger ages than those dEs in the center of Virgo, which are pressure supported, often have boxy isophotes and are older. Ram pressure stripping, thus, explains the properties of the dEs located in the outskirts of Virgo. However, the dEs in the central cluster regions, which have lost their angular momentum, must have suffered a more violent transformation. A combination of ram pressure stripping and harassment is not enough to remove the rotation and the spiral/disky structures of these galaxies. We find that on the the Faber-Jackson and the Fundamental Plane relations dEs deviate from the trends of massive elliptical galaxies towards the position of dark matter dominated systems such as the dwarf spheroidal satellites of the Milky Way and M31. Both, rotationally and pressure supported dEs, however, populate the same region in these diagrams. This indicates that dEs have a non-negligible dark matter fraction within their half light radius.
I have combined the Emsellem et al. ATLAS3D rotation measures of a large sample of early-type galaxies with HST-based classifications of their central structure to characterize the rotation velocities of galaxies with cores. Core galaxies rotate slowly, while power-law galaxies (galaxies that lack cores) rotate rapidly, confirming the analysis of Faber et al. Significantly, the amplitude of rotation sharply discriminates between the two types in the -19 > Mv > -22 domain over which the two types coexist. The slow rotation in the small set of core galaxies with Mv > -20, in particular, brings them into concordance with the more massive core galaxies. The ATLAS3D fast-rotating and slow-rotating early-type galaxies are essentially the same as power-law and core galaxies, respectively, or the Kormendy & Bender two families of elliptical galaxies based on rotation, isophote shape, and central structure. The ATLAS3D fast rotators do include roughly half of the core galaxies, but their rotation-amplitudes are always at the lower boundary of that subset. Essentially all core galaxies have ATLAS3D rotation-amplitudes lambda_(R_e/2) <= 0.25, while all galaxies with lambda_(R_e/2) > 0.25 and figure eccentricity > 0.2 lack cores. Both figure rotation and the central structure of early-type galaxies should be used together to separate systems that appear to have formed from wet versus dry mergers.
Using the data products of the Chandra Galaxy Atlas (Kim et al. 2019a), we have investigated the radial profiles of the hot gas temperature in 60 early type galaxies. Considering the characteristic temperature and radius of the peak, dip, and break (when scaled by the gas temperature and virial radius of each galaxy), we propose a universal temperature profile of the hot halo in ETGs. In this scheme, the hot gas temperature peaks at RMAX = 35 +/- 25 kpc (or ~0.04 RVIR) and declines both inward and outward. The temperature dips (or breaks) at RMIN (or RBREAK) = 3 - 5 kpc (or ~0.006 RVIR). The mean slope between RMIN (RBREAK) and RMAX is 0.3 +/- 0.1. Allowing for selection effects and observational limits, we find that the universal temperature profile can describe the temperature profiles of 72% (possibly up to 82%) of our ETG sample. The remaining ETGs (18%) with irregular or monotonically declining profiles do not fit the universal profile and require another explanation. The temperature gradient inside RMIN (RBREAK) varies widely, indicating different degrees of additional heating at small radii. Investigating the nature of the hot core (HC with a negative gradient inside RMIN), we find that HC is most clearly visible in small galaxies. Searching for potential clues associated with stellar, AGN feedback, and gravitational heating, we find that HC may be related to recent star formation. But we see no clear evidence that AGN feedback and gravitational heating play any significant role for HC.
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