4,027 research outputs found
Feedback in the local LBG Analog Haro 11 as probed by far-UV and X-ray observations
We have re-analyzed FUSE data and obtained new Chandra observations of Haro
11, a local (D_L=88 Mpc) UV luminous galaxy. Haro 11 has a similar far-UV
luminosity (10^10.3 L_\odot), UV surface brightness (10^9.4 L_\odot kpc^-2),
SFR, and metallicity to that observed in Lyman Break Galaxies (LBGs). We show
that Haro 11 has extended, soft thermal (kT~0.68 keV) X-ray emission with a
luminosity and size which scales with the physical properties (e.g. SFR,
stellar mass) of the host galaxy. An enhanced alpha/Fe, ratio of ~4 relative to
solar abundance suggests significant supernovae enrichment. These results are
consistent with the X-ray emission being produced in a shock between a
supernovae driven outflow and the ambient material. The FUV spectra show strong
absorption lines similar to those observed in LBG spectra. A blueshifted
absorption component is identified as a wind outflowing at ~200-280 km/s.
OVI\lambda\lambda1032,1038 emission, the dominant cooling mechanism for coronal
gas at T~10^5.5 K is also observed. If associated with the outflow, the
luminosity of the OVI emission suggests that <20% of the total mechanical
energy from the supernovae and solar winds is being radiated away. This implies
that radiative cooling through OVI is not significantly inhibiting the growth
of the outflowing gas. In contradiction to the findings of Bergvall et al 2006,
we find no convincing evidence of Lyman continuum leakage in Haro 11. We
conclude that the wind has not created a `tunnel' allowing the escape of a
significant fraction of Lyman continuum photons and place a limit on the escape
fraction of f_{esc}<2%. Overall, both Haro 11 and a previously observed LBG
analogue VV 114, provide an invaluable insight into the X-ray and FUV
properties of high redshift LBGs.Comment: Accepted for publication in ApJ, 40 pages, 17 figure
A New Sample of Low-mass Black Holes in Active Galaxies
We present an expanded sample of low-mass black holes (BHs) found in galactic
nuclei. Using standard virial mass techniques to estimate BH masses, we select
from the Fourth Data Release of the Sloan Digital Sky Survey all broad-line
active galaxies with masses < 2 x 10^6 M_sun. BHs in this mass regime provide
unique tests of the relationship between BHs and galaxies, since their
late-type galaxy hosts do not necessarily contain classical bulges.
Furthermore, they provide observational analogs of primordial seed BHs and are
expected, when merging, to provide strong gravitational signals for future
detectors such as LISA. From our preliminary sample of 19, we have increased
the total sample by an order of magnitude to 174, as well as an additional 55
(less secure) candidates. The sample has a median BH mass of = 1.3 x
10^6 M_sun, and in general the objects are radiating at high fractions of their
Eddington limits. We investigate the broad spectral properties of the sample;
55 are detected by \rosat, with soft X-ray luminosities in the range 10^40 to 7
x 10^43 ergs/sec. Much like the preliminary sample, these objects are
predominantly radio-quiet (R = f_6cm/f_4400A < 10), but 11 objects are detected
at 20 cm, with radio powers (10^21-10^23 W/Hz) that may arise from either star
formation or nuclear activity; only 1% of the sample is radio-loud. We further
confirm that, with =-19.3 and = 0.7 mag, the host galaxies are
low-mass, late-type systems. At least 40% show disk-like morphologies, and the
combination of host galaxy colors and higher-order Balmer absorption lines
indicate intermediate-age stellar populations in a subset of the sample.Comment: to appear in ApJ; 13 pages, 8 figure
Properties of H II Regions in the Centers of Nearby Galaxies
As part of an optical spectroscopic survey of nearby, bright galaxies, we
have identified a sample of over 200 emission-line nuclei having optical
spectra resembling those of giant extragalactic H II regions. Such "H II
nuclei," powered by young, massive stars, are found in a substantial fraction
of nearby galaxies, especially those of late Hubble type. This paper summarizes
the observational characteristics of H II nuclei, contrasts the variation of
their properties with Hubble type, and compares the nuclear H II regions with
those found in galaxy disks. Similarities and differences between H II nuclei
and luminous starburst nuclei are additionally noted.Comment: To appear in the Astrophysical Journal. LaTex, 37 pages including 15
postscript figures. AAStex macros include
Evidence for a Black Hole and Accretion Disk in the LINER NGC 4203
We present spectroscopic observations from the Hubble Space Telescope that
reveal for the first time the presence of a broad pedestal of Balmer-line
emission in the LINER galaxy NGC 4203. The emission-line profile is suggestive
of a relativistic accretion disk, and is reminiscent of double-peaked transient
Balmer emission observed in a handful of other LINERs. The very broad line
emission thus constitutes clear qualitative evidence for a black hole, and
spatially resolved narrow-line emission in NGC 4203 can be used to constrain
its mass, with M_BH less than 6 x 10^6 solar masses at 99.7% confidence. This
value implies a ratio of black-hole mass to bulge mass of less than
approximately 7 x 10^-4 in NGC 4203, which is less by a factor of ~3 - 9 than
the mean ratio obtained for other galaxies. The availability of an independent
constraint on central black-hole mass makes NGC4203 an important testbed for
probing the physics of weak active galactic nuclei. Assuming M_BH near the
detection limit, the ratio of observed luminosity to the Eddington luminosity
is approximately 10^-4. This value is consistent with advection-dominated
accretion, and hence with scenarios in which an ion torus irradiates an outer
accretion disk that produces the observed double-peaked line emission.
Follow-up observations will make it possible to improve the black-hole mass
estimate and study variability in the nuclear emission.Comment: 10 pages (LaTeX, AASTeX v4.0), 2 postscript figures, accepted for
publication in The Astrophysical Journal Letter
Understanding AGN-Host Connection in Partially Obscured Active Galactic Nuclei. Part I: The Nature of AGN+HII Composites
The goal of our serial papers is to examine the evolutionary connection
between AGN and star formation in its host galaxy in the partially obscured
AGNs (i.e., Seyfert 1.8 and 1.9 galaxies). Taking advantage of these galaxies,
the properties of both components can be studied together by direct
measurements. In this paper, we focus on the broad-line composite galaxies
(composite AGNs) which are located between the theoretical and empirical
separation lines in the [NII]/Ha vs. [OIII]/Hb diagram. These galaxies are
searched for from the composite galaxies provided by the SDSS DR4 MPA/JHU
catalogs. After re-analyze the spectra, we perform a fine classification for
the 85 composite AGNs in terms of the BPT diagrams. All the objects located
below the three theoretical separation lines are associated with a young
stellar population (<1Gyrs), while either a young or old stellar population is
identified in the individual multiply-classified object. The
multiply-classified objects with a very old stellar population are located in
the LINER region in the [OI]/Ha vs. [OIII]/Hb diagram. We then consider the
connection between AGN and star formation to derive the key results. The
Eddington ratio inferred from the broad Ha emission, the age of the stellar
population of AGN's host as assessed by D_n(4000), and the line ratio [OI]/Ha
are found to be related with each other. These relations strongly support the
evolutionary scenario in which AGNs evolve from high L/L_Edd state with soft
spectrum to low L/L_Edd state with hard spectrum as young stellar population
ages and fades. The significant correlation between the line ratio [OI]/Ha and
D_n(4000) leads us to suggest that the line ratio could be used to trace the
age of stellar population in type I AGNs.Comment: 39 pages, 11 figures, 1 table, accepted by Ap
Cold gas in the Intra Cluster Medium: implications for flow dynamics and powering optical nebulae
We show that the mechanical energy injection rate generated as the
intra-cluster medium (ICM) flows around cold clouds may be sufficient to power
the optical and near infra-red emission of nebulae observed in the central
regions of a sample of seven galaxy clusters. The energy injection rate is
extremely sensitive to the velocity difference between the ICM and cold clouds,
which may help to explain why optical and infra-red luminosity is often larger
than expected in systems containing AGNs. We also find that mass recycling is
likely to be important for the dynamics of the ICM. This effect will be
strongest in the central regions of clusters where there is more than enough
cold gas for its evaporation to contribute significantly to the density of the
hot phase.Comment: 8 pages, 2 figures, accepted for publication in MNRA
Search for clusters at high redshift - I. Candidate Lya emitters near 1138-262 at z=2.2
Radio, optical and X-ray observations of the powerful radio galaxy PKS
1138-262 at z=2.156 have suggested that this galaxy is a massive galaxy in the
center of a forming cluster. We have imaged 1138-262 and the surrounding 38
square arcminute field with the Very Large Telescope in a broad band and a
narrow band encompassing the redshifted Lya emission. We detect 50 objects with
rest equivalent width larger than 20 A and a luminous, highly extended Lya halo
around 1138-262. If the radio galaxy is at the center of a forming cluster,
these objects are candidate Lya emitting cluster galaxies.Comment: Accepted for publication in A&A as Letter, 4 pages, 4 figure
A Search for Ultraviolet Emission from LINERs
We have obtained Hubble Space Telescope WFPC2 2200 A and optical V-band
images of 20 low-luminosity active galactic nuclei, most of which are
spectroscopically classified as LINERs, in order to search for a possible
photoionizing continuum. Six (30%) of the galaxies are detected in the UV. Two
of the detected galaxies (NGC 3642 and NGC 4203) have compact, unresolved
nuclear UV sources, while the remaining four UV sources (in NGC 4569, NGC 5005,
NGC 6500, and NGC 7743) are spatially extended. Combining our sample with that
of Maoz et al. (1995), we find that the probability of detection of a nuclear
UV source is greatest for galaxies having low internal reddening and low
inclination, and we conclude that dust obscuration is the dominant factor
determining whether or not a UV source is detected. Large emission-line
equivalent widths and the presence of broad-line emission also increase the
likelihood of detection of nuclear UV emission. Our results suggest that the
majority of LINERs harbor obscured nuclear UV sources, which may be either
accretion-powered active nuclei or young star clusters. Under the assumption
that the compact UV sources in NGC 3642 and NGC 4203 have nonstellar power-law
spectra extending into the extreme ultraviolet, the extrapolated ionizing
fluxes are sufficiently strong to photoionize the narrow-line regions of these
objects. The V-band images of many galaxies in our sample reveal remarkably
strong dust lanes which may be responsible for obscuring some UV sources.Comment: 25 pages, 4 figures, 3 tables, LaTeX, AASTeX v4.0 style file,
accepted for publication in The Astrophysical Journal, additional figures
available at http://astro.berkeley.edu/~barth/papers/u
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