40 research outputs found
A photometric analysis of Abell 1689: two-dimensional multi-structure decomposition, morphological classification, and the Fundamental Plane
We present a photometric analysis of 65 galaxies in the rich cluster Abell
1689 at , using the Hubble Space Telescope Advanced Camera for Surveys
archive images in the rest-frame -band. We perform two-dimensional
multi-component photometric decomposition of each galaxy adopting different
models of the surface-brightness distribution. We present an accurate
morphological classification for each of the sample galaxies. For 50 early-type
galaxies, we fit both a de Vaucouleurs and S\'ersic law; S0s are modelled by
also including a disc component described by an exponential law. Bars of SB0s
are described by the profile of a Ferrers ellipsoid. For the 15 spirals, we
model a S\'ersic bulge, exponential disc, and, when required, a Ferrers bar
component. We derive the Fundamental Plane by fitting 40 early-type galaxies in
the sample, using different surface-brightness distributions. We find that the
tightest plane is that derived by S\'ersic bulges. We find that bulges of
spirals lie on the same relation. The Fundamental Plane is better defined by
the bulges alone rather than the entire galaxies. Comparison with local samples
shows both an offset and rotation in the Fundamental Plane of Abell 1689.Comment: 53 pages, 71 figures, MNRAS in pres
A Fundamental Relation between Compact Stellar Nuclei, Supermassive Black Holes, and Their Host Galaxies
Imaging surveys with the Hubble Space Telescope (HST) have shown that 50â80% of low- and intermediate-luminosity galaxies contain a compact stellar nucleus at their center, regardless of host galaxy morphological type. We combine HST imaging for early-type galaxies from the ACS Virgo Cluster Survey with ground-based long-slit spectra from KPNO to show that the masses of compact stellar nuclei in Virgo Cluster galaxies obey a tight correlation with the masses of the host galaxies. The same correlation is obeyed by the supermassive black holes (SBHs) found in predominantly massive galaxies. The compact stellar nuclei in the Local Group galaxies M33 and NGC 205 are also found to fall along this same scaling relation. These results indicate that a generic by-product of galaxy formation is the creation of a central massive object (CMO) â either a SBH or a compact stellar nucleus â that contains a mean fraction, 0.2%, of the total galactic mass. In galaxies with masses greater than Mgal a few 1010Mâ, SBHs appear to be the dominant mode of CMO formation
On the distribution of galaxy ellipticity in clusters
open4We study the distribution of projected ellipticity n(Δ) for galaxies in a sample of 20 rich (Richness ℠2) nearby (z 0.4), therefore it is not a consequence of the increasing fraction of round slow rotator galaxies near cluster centers. Furthermore, the Δ-R relation persists for just smooth flattened galaxies and for galaxies with deVaucouleurs-like light profiles, suggesting that the variation of the spiral fractionwith radius is not the underlying cause of the trend. We interpret our findings in light of the classification of early type galaxies (ETGs) as fast and slow rotators. We conclude that the observed trend of decreasing Δ towards the centres of clusters is evidence for physical effects in clusters causing fast rotator ETGs to have a lower average intrinsic ellipticity near the centres of rich clusters.openD'Eugenio F.; Houghton R.C.W.; Davies R.L.; Dalla Bonta' E.D'Eugenio, F.; Houghton, R. C. W.; Davies, R. L.; Dalla Bonta', E
A New Sample of Gamma-Ray Emitting Jetted Active Galactic Nuclei
We considered the fourth catalog of gamma-ray point sources produced by the
Fermi Large Area Telescope (LAT) and selected only jetted active galactic
nuclei (AGN) or sources with no specific classification, but with a
low-frequency counterpart. Our final list is composed of 2980 gamma-ray point
sources. We then searched for optical spectra in all the available literature
and publicly available databases, to measure redshifts and to confirm or change
the original LAT classification. Our final list of gamma-ray emitting jetted
AGN is composed of BL Lac Objects (40%), flat-spectrum radio quasars (23%),
misaligned AGN (2.8%), narrow-line Seyfert 1, Seyfert, and low-ionization
nuclear emission-line region galaxies (1.9%). We also found a significant
number of objects changing from one type to another, and vice versa
(changing-look AGN, 1.1%). About 30% of gamma-ray sources still have an
ambiguous classification or lack one altogether.Comment: 18 pages, 5 figures, 1 Table. Accepted for publication on Universe,
Special Issue "Black Holes and Relativistic Jets", edited by I. Dutan and N.
R. MacDonald. This preprint contains only the main text. The full tables A1
and A2 are available on the journal web site
(https://www.mdpi.com/2218-1997/8/11/587
Near-infrared spectroscopic indices for unresolved stellar populations. III. Composite indices definition as age and metallicity tracers and model comparison
Recent advances in the stellar population studies of unresolved galaxies in the NIR domain demonstrated that it contains several line-strength indices to be potentially used as diagnostics for stellar population properties. Reduction of the extinction and possibility to disentangle different stellar populations dominating different spectral ranges are obviously beneficial. To this aim, we have investigated the connections between 19 Lick/IDS indices and 39 NIR indices measured in the central regions of 32 galaxies observed with X-shooter. We adopted a systematic approach deriving a correlation matrix using all the optical and NIR indices measured for the galaxies and building new NIR composite indices to maximise their correlations with the best age and metallicity optical tracers. We found that the new T1 and [AlFeCr] composite indices are promising age and metallicity diagnostics in NIR, respectively. We finally tested the T1 and [AlFeCr] indices with the predictions of simple stellar populations models and we found that models show a general agreement with the data. Some fine tuning and further comparison between models and data, that are now largely available, is necessary to reach the prediction level of the optical line-strength indices
The Cepheid Distance to the Narrow-Line Seyfert 1 Galaxy NGC 4051
We derive a distance of ~Mpc (~mag) to
the archetypal narrow-line Seyfert 1 galaxy NGC 4051 based on Cepheid
Period--Luminosity relations and new Hubble Space Telescope multiband imaging.
We identify 419 Cepheid candidates and estimate the distance at both optical
and near-infrared wavelengths using subsamples of precisely-photometered
variables (123 and 47 in the optical and near-infrared subsamples,
respectively). We compare our independent photometric procedures and
distance-estimation methods to those used by the SH0ES team and find agreement
to 0.01~mag. The distance we obtain suggests an Eddington ratio for NGC 4051, typical of narrow-line Seyfert 1 galaxies, unlike
the seemingly-odd value implied by previous distance estimates. We derive a
peculiar velocity of ~km~s for NGC 4051, consistent with the
overall motion of the Ursa Major Cluster in which it resides. We also revisit
the energetics of the NGC 4051 nucleus, including its outflow and mass
accretion rates.Comment: 15 pages, 12 figures, 6 tables, accepted for publication in Ap
Velocity-resolved Reverberation Mapping of Five Bright Seyfert 1 Galaxies
We present the first results from a reverberation-mapping campaign undertaken during the first half of 2012, with additional data on one active galactic nucleus (AGN) (NGC 3227) from a 2014 campaign. Our main goals are (1) to determine the black hole masses from continuum-HÎČ reverberation signatures, and (2) to look for velocity-dependent time delays that might be indicators of the gross kinematics of the broad-line region. We successfully measure HÎČ time delays and black hole masses for five AGNs, four of which have previous reverberation mass measurements. The values measured here are in agreement with earlier estimates, though there is some intrinsic scatter beyond the formal measurement errors. We observe velocity-dependent HÎČ lags in each case, and find that the patterns have changed in the intervening five years for three AGNs that were also observed in 2007
AGN STORM 2. I. First results: A Change in the Weather of Mrk 817
We present the first results from the ongoing, intensive, multiwavelength monitoring program of the luminous Seyfert 1 galaxy Mrk 817. While this active galactic nucleus was, in part, selected for its historically unobscured nature, we discovered that the X-ray spectrum is highly absorbed, and there are new blueshifted, broad, and narrow UV absorption lines, which suggest that a dust-free, ionized obscurer located at the inner broad-line region partially covers the central source. Despite the obscuration, we measure UV and optical continuum reverberation lags consistent with a centrally illuminated ShakuraâSunyaev thin accretion disk, and measure reverberation lags associated with the optical broad-line region, as expected. However, in the first 55 days of the campaign, when the obscuration was becoming most extreme, we observe a de-coupling of the UV continuum and the UV broad emission-line variability. The correlation recovered in the next 42 days of the campaign, as Mrk 817 entered a less obscured state. The short C IV and Lyα lags suggest that the accretion disk extends beyond the UV broad-line region. Unified
AGN STORM 2. IV. Swift X-Ray and Ultraviolet/Optical Monitoring of Mrk 817
The AGN STORM 2 campaign is a large, multiwavelength reverberation mapping project designed to trace out the structure of Mrk 817 from the inner accretion disk to the broad emission line region and out to the dusty torus. As part of this campaign, Swift performed daily monitoring of Mrk 817 for approximately 15 months, obtaining observations in X-rays and six UV/optical filters. The X-ray monitoring shows that Mrk 817 was in a significantly fainter state than in previous observations, with only a brief flare where it reached prior flux levels. The X-ray spectrum is heavily obscured. The UV/optical light curves show significant variability throughout the campaign and are well correlated with one another, but uncorrelated with the X-rays. Combining the Swift UV/optical light curves with Hubble Space Telescope UV continuum light curves, we measure interband continuum lags, Ï(λ), that increase with increasing wavelength roughly following Ï(λ) â λ 4/3, the dependence expected for a geometrically thin, optically thick, centrally illuminated disk. Modeling of the light curves reveals a period at the beginning of the campaign where the response of the continuum is suppressed compared to later in the light curveâthe light curves are not simple shifted and scaled versions of each other. The interval of suppressed response corresponds to a period of high UV line and X-ray absorption, and reduced emission line variability amplitudes. We suggest that this indicates a significant contribution to the continuum from the broad-line region gas that sees an absorbed ionizing continuum