265 research outputs found
Precise Black Hole Masses From Megamaser Disks: Black Hole-Bulge Relations at Low Mass
The black hole (BH)-bulge correlations have greatly influenced the last
decade of effort to understand galaxy evolution. Current knowledge of these
correlations is limited predominantly to high BH masses (M_BH> 10^8 M_sun) that
can be measured using direct stellar, gas, and maser kinematics. These objects,
however, do not represent the demographics of more typical L< L* galaxies. This
study transcends prior limitations to probe BHs that are an order of magnitude
lower in mass, using BH mass measurements derived from the dynamics of H_2O
megamasers in circumnuclear disks. The masers trace the Keplerian rotation of
circumnuclear molecular disks starting at radii of a few tenths of a pc from
the central BH. Modeling of the rotation curves, presented by Kuo et al.
(2010), yields BH masses with exquisite precision. We present stellar velocity
dispersion measurements for a sample of nine megamaser disk galaxies based on
long-slit observations using the B&C spectrograph on the Dupont telescope and
the DIS spectrograph on the 3.5m telescope at Apache Point. We also perform
bulge-to-disk decomposition of a subset of five of these galaxies with SDSS
imaging. The maser galaxies as a group fall below the M_BH-sigma* relation
defined by elliptical galaxies. We show, now with very precise BH mass
measurements, that the low-scatter power-law relation between M_BH and sigma*
seen in elliptical galaxies is not universal. The elliptical galaxy M_BH-sigma*
relation cannot be used to derive the BH mass function at low mass or the
zeropoint for active BH masses. The processes (perhaps BH self-regulation or
minor merging) that operate at higher mass have not effectively established an
M_BH-sigma* relation in this low-mass regime.Comment: 21 pages, 14 figures, accepted for publication in the Astrophysical
Journa
AINUR: Atlas of Images of NUclear Rings
We present the most complete atlas of nuclear rings to date. We include 113
rings found in 107 galaxies, six of which are elliptical galaxies, five are
highly inclined disc galaxies, 18 are unbarred disc galaxies, and 78 are barred
disc galaxies. Star-forming nuclear rings occur in 20% of disc galaxies with
types between T=-3 and T=7. We aim to explore possible relationships between
the size and morphology of the rings and various galactic parameters. We
produce colour index and structure maps, as well as Halpha and Paalpha
continuum-subtracted images from HST archival data. We derive ellipticity
profiles from H-band 2MASS images in order to detect bars and find their metric
parameters. We measure the non-axisymmetric torque parameter, Qg, and search
for correlations between bar, ring metric parameters, and Qg.
Our atlas of nuclear rings includes star-forming and dust rings. Nuclear
rings span a range from a few tens of parsecs to a few kiloparsecs in radius.
Star-forming nuclear rings can be found in a wide range of morphological types,
from S0 to Sd, with a peak in the distribution between Sab and Sb, and without
strong preference for barred galaxies. Dust nuclear rings are found in
elliptical and S0 galaxies. For barred galaxies, the maximum radius that a
nuclear ring can reach is a quarter of the bar radius. We found a nearly random
distribution of PA offsets between nuclear rings and bars. There is some
evidence that nuclear ring ellipticity is limited by bar ellipticity. We
confirm that the maximum relative size of a star-forming nuclear ring is
inversely proportional to the non-axisymmetric torque parameter, Qg, and that
the origin of nuclear rings, even the ones in non-barred hosts, are closely
linked to the existence of dynamical resonances.Comment: Accepted for publication in MNRAS. A full resolution version of the
manuscript with high resolution figures can be found at
http://www.iac.es/folleto/research/preprints
The Host Galaxies of Low-mass Black Holes
Using HST observations of 147 host galaxies of low-mass black holes (BHs), we
systematically study the structures and scaling relations of these active
galaxies. Our sample is selected to have central BHs with virial masses
~10^5-10^6 solar mass. The host galaxies have total I-band magnitudes of
-23.2<M_I<-18.8 mag and bulge magnitudes of -22.9<M_I<-16.1 mag. Detailed
bulge-disk-bar decompositions with GALFIT show that 93% of the galaxies have
extended disks, 39% have bars and 5% have no bulges at all at the limits of our
observations. Based on the Sersic index and bulge-to-total ratio, we conclude
that the majority of the galaxies with disks are likely to contain pseudobulges
and very few of these low-mass BHs live in classical bulges. The fundamental
plane of our sample is offset from classical bulges and ellipticals in a way
that is consistent with the scaling relations of pseudobulges. The sample has
smaller velocity dispersion at fixed luminosity in the Faber-Jackson plane,
compared with classical bulges and elliptical galaxies. The galaxies without
disks are structurally more similar to spheroidals than to classical bulges
according to their positions in the fundamental plane, especially the
Faber-Jackson projection. Overall, we suggest that BHs with mass < 10^6 solar
mass live in galaxies that have evolved secularly over the majority of their
history. A classical bulge is not a prerequisite to host a black hole.Comment: 49 pages, 9 figures, accepted by Ap
On the Correlations between Galaxy Properties and Supermassive Black Hole Mass
We use a large sample of upper limits and accurate estimates of supermassive
black holes masses coupled with libraries of host galaxy velocity dispersions,
rotational velocities and photometric parameters extracted from Sloan Digital
Sky Survey i-band images to establish correlations between the SMBH and host
galaxy parameters. We test whether the mass of the black hole, MBH, is
fundamentally driven by either local or global galaxy properties. We explore
correlations between MBH and stellar velocity dispersion sigma, bulge
luminosity, bulge mass Sersic index, bulge mean effective surface brightness,
luminosity of the galaxy, galaxy stellar mass, maximum circular velocity Vc,
galaxy dynamical and effective masses. We verify the tightness of the MBH-sigma
relation and find that correlations with other galaxy parameters do not yield
tighter trends. We do not find differences in the MBH-sigma relation of barred
and unbarred galaxies. The MBH-sigma relation of pseudo-bulges is also coarser
and has a different slope than that involving classical bulges. The MBH-bulge
mass is not as tight as the MBH-sigma relation, despite the bulge mass proving
to be a better proxy of MBH than bulge luminosity. We find a rather poor
correlation between MBH and Sersic index suggesting that MBH is not related to
the bulge light concentration. The correlations between MBH and galaxy
luminosity or mass are not a marked improvement over the MBH sigma relation. If
Vc is a proxy for the dark matter halo mass, the large scatter of the MBH-Vc
relation then suggests that MBH is more coupled to the baryonic rather than the
dark matter. We have tested the need for a third parameter in the MBH scaling
relations, through various linear correlations with bulge and galaxy
parameters, only to confirm that the fundamental plane of the SMBH is mainly
driven by sigma, with a small tilt due to the effective radius. (Abridged)Comment: 32 pages, 18 figures, 6 tables, accepted for publication in MNRA
Point-of-Care Tests for Hepatitis B Are Associated with A Higher Linkage to Care and Lower Cost Compared to Venepuncture Sampling During Outreach Screenings in an Asian Migrant Population
Background: This study compares venepuncture versus point-of-care (POC) HBsAg tests on screening cost and linkage to care in prospective outreach screenings in an Asian population in three major cities in Belgium between 10/2014 and 5/2018. Methods: Two community outreach screening programs were organised between 10/2014 and 5/2018. The first screening program used venepuncture and serologic testing for HBsAg. In the second program, HBsAg was tested in finger stick blood POC tests. Positive results were confirmed during outpatient visits with serologic testing. Linkage to care was defined as having received specialist care follow-up with at least one abdominal ultrasound within three months of screening. Results: For 575 participating individuals, 571 valid results were obtained, 456 with venepuncture, and 115 using POC testing. Overall HBsAg seroprevalence was 6.8%. Linkage to care was higher when using POC testing compared to venepuncture (86% or n = 6/7 versus 34% or n = 11/32; p = 0.020). The POC screening program was economically more attractive with a total cost of € 1,461.8 or € 12.7 per person screened compared to € 24,819 or € 54.0 per person screened when using venepuncture testing. Results and an appointment for specialist care follow-up were given onsite with POC testing, while with venepuncture testing; results were sent within 20-45 days. Conclusion: In an Asian migrant population in Belgium with an HBsAg seroprevalence of 6.8%, HBV screening based on POC tests resulted in lower costs per person screened (76.5% lower), and higher linkage to care (2.5 times)
Radial Distribution of Near-UV Flux in Disc Galaxies in the range 0<z<1
(Abridged) The goal of this paper is to quantify the changes on the SF
distribution within the disc galaxies in the last ~8 Gyr. We use as a proxy for
the SF radial profile the Near-UV surface brightness distributions, allowing
suitably for extinction. We compare the effective radii (R_eff) and
concentration of the flux distribution in the rest-frame Near-UV for a sample
of 270 galaxies in the range 0<z<1. This radial distribution is compared to
that measured in the rest-frame B-band, which traces older stellar populations.
The analysis is performed using deep, high resolution, multi-band images from
GALEX, SDSS, and HST/ACS - GOODS-South. The relation R_eff(NUV)- M* suffers a
moderate change between z~1 and z~0: at a fixed stellar mass of 1E10 M_sun,
galaxies increase their effective radii by a factor 1.18+/-0.06. Median
profiles in NUV show signs of truncation at R~R_eff, and median colour profiles
(NUV-B) show a minimum (a "bluest" point) also around R~1-1.5 R_eff. The
distributions of NUV flux are more compact at z~1 than nowadays, in terms of
the fraction of flux enclosed in a specific radius (in kpc). Our results
indicate that the SF surface density has decreased dramatically in discs since
z~1, and this decline has been more intense in the central parts (<~R_eff) of
the galaxies. In addition, our data suggest that the bulges/pseudo-bulges have
grown in surface brightness with regard to the discs since z~1.Comment: 26 pages, 21 figures, accepted for publication in Astronomy &
Astrophysics on March 21s
Star Formation History at the Centers of Lenticular Galaxies with Bars and Purely Exponential Outer Disks from SAURON Data
We have investigated the stellar population properties in the central regions
of a sample of lenticular galaxies with bars and single-exponential outer
stellar disks using the data from the SAURON integral-field spectrograph
retrieved from the open Isaac Newton Group Archive. We have detected chemically
decoupled compact stellar nuclei with a metallicity twice that of the stellar
population in the bulges in seven of the eight galaxies. A starburst is
currently going on at the center of the eighth galaxy and we have failed to
determine the stellar population properties from its spectrum. The mean stellar
ages in the chemically decoupled nuclei found range from 1 to 11 Gyr. The
scenarios for the origin of both decoupled nuclei and lenticular galaxies as a
whole are discussed.Comment: 10 pages, 4 figures, a slightly edited version of the paper published
by Astronomy Letters, v. 37, no.1, 201
The detection of stellar velocity dispersion drops in the central regions of five isolated Seyfert spirals
We analyze the kinematics of the central regions of five isolated Seyfert
spiral galaxies from the DEGAS sample (four with new data presented in this
paper, IC184, UGC3223, NGC2639, NGC6814, and NGC6951 from our previous data),
by using long slit spectroscopy in the CaII triplet range (at ~ 8600 A)
obtained with a 4m-class telescope. A drop of the velocity dispersions in the
innermost 1-3 arcsec is observed in four of them, and hinted in the remaining
galaxy (NGC6814). The available HST images for our sample together with another
nine galaxies with reported velocity dispersion drops, are also used to
investigate the presence of morphological inner structures at the scales of the
kinematical drops. Evidence for disk-like shapes is found in 12 out of the 14
cases. The only exceptions are NGC6814 and NGC6951. Existing N-body simulations
including stars, gas and star formation predict that such a drop is most
probably due to a young stellar population born from dynamically cold gas
accreted in a circumnuclear disk formed during an episode of central gas
accretion driven by a bar. The equivalent widths of the Calcium triplet lines
for our 5 galaxies have been measured. Even if the profiles could be formally
consistent with constant EW(CaT) values, they seem to indicate the presence of
a local maximum in the regions corresponding spatially to the drops; if
confirmed, this would imply the presence of a different stellar population,
whose properties could help constraining the models.Comment: A&A accepted for publicatio
Enhanced dust heating in the bulges of early-type spiral galaxies
Stellar density and bar strength should affect the temperatures of the cool
(T ~ 20-30 K) dust component in the inner regions of galaxies, which implies
that the ratio of temperatures in the circumnuclear regions to the disk should
depend on Hubble type. We investigate the differences between cool dust
temperatures in the central 3 kpc and disk of 13 nearby galaxies by fitting
models to measurements between 70 and 500 microns. We attempt to quantify
temperature trends in nearby disk galaxies, with archival data from
Spitzer/MIPS and new observations with Herschel/SPIRE, which were acquired
during the first phases of the Herschel observations for the KINGFISH (key
insights in nearby galaxies: a far-infrared survey with Herschel) sample. We
fit single-temperature modified blackbodies to far-infrared and submillimeter
measurements of the central and disk regions of galaxies to determine the
temperature of the component(s) emitting at those wavelengths. We present the
ratio of central-region-to-disk-temperatures of the cool dust component of 13
nearby galaxies as a function of morphological type. We find a significant
temperature gradient in the cool dust component in all galaxies, with a mean
center-to-disk temperature ratio of 1.15 +/- 0.03. The cool dust temperatures
in the central ~3 kpc of nearby galaxies are 23(+/-3)% hotter for morphological
types earlier than Sc, and only 9(+/-3)% hotter for later types. The
temperature ratio is also correlated with bar strength, with only strongly
barred galaxies having a ratio over 1.2. The strong radiation field in the high
stellar density of a galactic bulge tends to heat the cool dust component to
higher temperatures, at least in early-type spirals with relatively large
bulges, especially when paired with a strong bar.Comment: Accepted for publication on the A&A Herschel Special Issu
The Fueling and Evolution of AGN: Internal and External Triggers
In this chapter, I review the fueling and evolution of active galactic nuclei
(AGN) under the influence of internal and external triggers, namely intrinsic
properties of host galaxies (morphological or Hubble type, color, presence of
bars and other non-axisymmetric features, etc) and external factors such as
environment and interactions. The most daunting challenge in fueling AGN is
arguably the angular momentum problem as even matter located at a radius of a
few hundred pc must lose more than 99.99 % of its specific angular momentum
before it is fit for consumption by a BH. I review mass accretion rates,
angular momentum requirements, the effectiveness of different fueling
mechanisms, and the growth and mass density of black BHs at different epochs. I
discuss connections between the nuclear and larger-scale properties of AGN,
both locally and at intermediate redshifts, outlining some recent results from
the GEMS and GOODS HST surveys.Comment: Invited Review Chapter to appear in LNP Volume on "AGN Physics on All
Scales", Chapter 6, in press. 40 pages, 12 figures. Typo in Eq 5 correcte
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