69 research outputs found
Extragalactic H_2O masers and X-ray absorbing column densities
Having conducted a search for the 22 GHz water vapor line towards galaxies
with nuclear activity, large nuclear column densities or high infrared
luminosities, we present H_2O spectra for NGC2273, UGC5101 and NGC3393 with
isotropic luminosities of 7, 1500, and 400 L_sun. The H_2O maser in UGC5101 is
by far the most luminous yet found in an ultraluminous infrared galaxy. NGC3393
reveals the classic spectrum of a `disk maser', represented by three distinct
groups of Doppler components. As in all other known cases except NGC4258, the
rotation velocity of the putative masing disk is well below 1000 km/s. Based on
the literature and archive data, X-ray absorbing column densities are compiled
for the 64 galaxies with reported maser sources beyond the Magellanic Clouds.
For NGC2782 and NGC5728, we present Chandra archive data that indicate the
presence of an active galactic nucleus in both galaxies. The correlation
between absorbing column and H_2O emission is analyzed. There is a striking
difference between kilo- and megamasers with megamasers being associated with
higher column densities. All kilomasers (L_H_2O < 10 L_sun) except NGC2273 and
NGC5194 are Compton-thin, i.e. their absorbing columns are < 10^24 cm^-2. Among
the H_2O megamasers, 50% arise from Compton-thick and 85% from heavily obscured
(> 10^23 cm^-2) active galactic nuclei. These values are not larger but
consistent with those from samples of Seyfert 2 galaxies not selected on the
basis of maser emission. The similarity in column densities can be explained by
small deviations in position between maser spots and nuclear X-ray source and a
high degree of clumpiness in the circumnuclear interstellar medium.Comment: 16 pages, 7 figures, 5 tables. Accepted for publication in A&
Galactic-Scale Outflow and Supersonic Ram-Pressure Stripping in the Virgo Cluster Galaxy NGC 4388
The Hawaii Imaging Fabry-Perot Interferometer (HIFI) on the University of
Hawaii 2.2m telescope was used to map the Halpha and [O III] 5007 A
emission-line profiles across the entire disk of the edge-on Sb galaxy NGC
4388. We confirm a rich complex of highly ionized gas that extends ~4 kpc above
the disk of this galaxy. Low-ionization gas associated with star formation is
also present in the disk. Evidence for bar streaming is detected in the disk
component and is discussed in a companion paper (Veilleux, Bland-Hawthorn, &
Cecil 1999; hereafter VBC). Non-rotational blueshifted velocities of 50 - 250
km/s are measured in the extraplanar gas north-east of the nucleus. The
brighter features in this complex tend to have more blueshifted velocities. A
redshifted cloud is also detected 2 kpc south-west of the nucleus. The velocity
field of the extraplanar gas of NGC 4388 appears to be unaffected by the
inferred supersonic (Mach number M ~ 3) motion of this galaxy through the ICM
of the Virgo cluster. We argue that this is because the galaxy and the high-|z|
gas lie behind a Mach cone with opening angle ~ 80 degrees. The shocked ICM
that flows near the galaxy has a velocity of ~ 500 km/s and exerts insufficient
ram pressure on the extraplanar gas to perturb its kinematics. We consider
several explanations of the velocity field of the extraplanar gas. Velocities,
especially blueshifted velocities on the N side of the galaxy, are best
explained as a bipolar outflow which is tilted by > 12 degrees from the normal
to the disk. The observed offset between the extraplanar gas and the radio
structure may be due to buoyancy or refractive bending by density gradients in
the halo gas. Velocity substructure in the outflowing gas also suggests an
interaction with ambient halo gas.Comment: 29 pages including 5 figures, Latex, requires aaspp4.sty, to appear
in ApJ, 520 (July 20, 1999 issue
X-ray Spectral Survey with XMM--Newton of a Complete Sample of Nearby Seyfert Galaxies
Results obtained from an X-ray spectral survey of nearby Seyfert galaxies
using XMM--Newton are reported. The sample was optically selected, well
defined, complete in B mag, and distance limited: it consists of the nearest
(D<22 Mpc) 27 Seyfert galaxies (9 of type 1, 18 of type 2) taken from the Ho et
al. (1997) sample. This is one of the largest atlases of hard X-ray spectra of
low-L active galaxies ever assembled. All nuclear sources except two Sey 2s are
detected between 2-10 keV, half for the first time ever, and average spectra
are obtained for all of them. Nuclear luminosities reach values down to 10**38
erg/s. The shape of the distribution of X-ray parameters is affected by the
presence of Compton-thick objects (> 30% among type 2s). The latter have been
identified either directly from their intense FeK line and flat X-ray spectra,
or indirectly with flux diagnostic diagrams which use isotropic indicators.
After taking into account these highly absorbed sources, we find that (i) the
intrinsic X-ray spectral properties (i.e., spectral shapes and luminosities
above 2 keV) are consistent between type 1 and type 2 Sey, as expected from
``unified models'', (ii) Sey galaxies as a whole are distributed fairly
continuously over the entire range of Nh, between 10**20 and 10**25 cm**-2, and
(iii) while Sey 1s tend to have lower Nh and Sey 2s tend to have the highest,
we find 30% and 10% exceptions, respectively. Overall the sample well
represents the average intrinsic X-ray spectral properties of nearby AGN,
including a proper estimate of the distribution of their absorbing columns.
Finally, we conclude that, with the exception of a few cases, the present study
agrees with predictions of unified models of Sey galaxies, and extends their
validity down to very low luminosities.Comment: 23 pages, 4 tables, 4 figures, 2 Appendices with 27 source spectra
and notes, to be published in the Astronomy & Astrophysics Journa
Supermassive Black Holes in Galactic Nuclei: Past, Present and Future Research
This review discusses the current status of supermassive black hole research,
as seen from a purely observational standpoint. Since the early '90s, rapid
technological advances, most notably the launch of the Hubble Space Telescope,
the commissioning of the VLBA and improvements in near-infrared speckle imaging
techniques, have not only given us incontrovertible proof of the existence of
supermassive black holes, but have unveiled fundamental connections between the
mass of the central singularity and the global properties of the host galaxy.
It is thanks to these observations that we are now, for the first time, in a
position to understand the origin, evolution and cosmic relevance of these
fascinating objects.Comment: Invited Review, 114 pages. Because of space requirements, this
version contains low resolution figures. The full resolution version can be
downloaded from http://www.physics.rutgers.edu/~lff/publications.htm
On the X-ray, optical emission line and black hole mass properties of local Seyfert galaxies
We investigate the relation between X-ray nuclear emission, optical emission
line luminosities and black hole masses for a sample of 47 Seyfert galaxies.
The sample, which has been selected from the Palomar optical spectroscopic
survey of nearby galaxies (Ho, Filippenko & Sargent 1997), covers a wide range
of nuclear powers, from L_{2-10 keV} ~ 10^{43} erg/s down to very low
luminosities (L_{2-10 keV} ~ 10^{38} erg/s). Best available data from Chandra,
XMM-Newton and, in a few cases, ASCA observations have been considered. Thanks
to the good spatial resolution available from these observations and a proper
modeling of the various spectral components, it has been possible to obtain
accurate nuclear X-ray luminosities not contaminated by off-nuclear sources
and/or diffuse emission. X-ray luminosities have then been corrected taking
into account the likely candidate Compton thick sources, which are a high
fraction (> 30%) among type 2 Seyferts in our sample. The main result of this
study is that we confirm strong linear correlations between 2-10 keV,
[OIII]\lambda5007, H_{alpha} luminosities which show the same slope as quasars
and luminous Seyfert galaxies, independent of the level of nuclear activity
displayed. Moreover, despite the wide range of Eddington ratios (L/L_{Edd})
tested here (six orders of magnitude, from 0.1 down to ~ 10^{-7}), no
correlation is found between the X-ray or optical emission line luminosities
and the black hole mass. Our results suggest that Seyfert nuclei in our sample
are consistent with being a scaled-down version of more luminous AGN.Comment: 17 pages, 10 figures, accepted by Astronomy and Astrophysic
The SAMI Galaxy Survey: revisiting galaxy classification through high-order stellar kinematics
Recent cosmological hydrodynamical simulations suggest that integral field spectroscopy can connect the high-order stellar kinematic moments h3 (~skewness) and h4 (~kurtosis) in galaxies to their cosmological assembly history. Here, we assess these results by measuring the stellar kinematics on a sample of 315 galaxies, without a morphological selection, using two-dimensional integral field data from the SAMI Galaxy Survey. Proxies for the spin parameter () and ellipticity () are used to separate fast and slow rotators; there exists a good correspondence to regular and non-regular rotators, respectively, as also seen in earlier studies. We confirm that regular rotators show a strong h3 versus anti-correlation, whereas quasi-regular and non-regular rotators show a more vertical relation in h3 and . Motivated by recent cosmological simulations, we develop an alternative approach to kinematically classify galaxies from their individual h3 versus signatures. Within the SAMI Galaxy Survey, we identify five classes of high-order stellar kinematic signatures using Gaussian mixture models. Class 1 corresponds to slow rotators, whereas Classes 2â5 correspond to fast rotators. We find that galaxies with similar {\lambda }_{{R}_{{\rm{e}}}}\mbox{--}{\epsilon }_{{\rm{e}}} values can show distinctly different {h}_{3}\mbox{--}V/\sigma signatures. Class 5 objects are previously unidentified fast rotators that show a weak h3 versus anti-correlation. From simulations, these objects are predicted to be disk-less galaxies formed by gas-poor mergers. From morphological examination, however, there is evidence for large stellar disks. Instead, Class 5 objects are more likely disturbed galaxies, have counter-rotating bulges, or bars in edge-on galaxies. Finally, we interpret the strong anti-correlation in h3 versus as evidence for disks in most fast rotators, suggesting a dearth of gas-poor mergers among fast rotators
The SAMI Galaxy Survey : spatially resolving the main sequence of star formation
We present the âŒ800 star formation rate maps for the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey based on Hâα emission maps, corrected for dust attenuation via the Balmer decrement, that are included in the SAMI Public Data Release 1. We mask out spaxels contaminated by non-stellar emission using the [Oâiii]/HâÎČ, [Nâii]/Hâα, [Sâii]/Hâα, and [Oâi]/Hâα line ratios. Using these maps, we examine the global and resolved star-forming main sequences of SAMI galaxies as a function of morphology, environmental density, and stellar mass. Galaxies further below the star-forming main sequence are more likely to have flatter star formation profiles. Early-type galaxies split into two populations with similar stellar masses and central stellar mass surface densities. The main-sequence population has centrally concentrated star formation similar to late-type galaxies, while galaxies >3Ï below the main sequence show significantly reduced star formation most strikingly in the nuclear regions. The split populations support a two-step quenching mechanism, wherein halo mass first cuts off the gas supply and remaining gas continues to form stars until the local stellar mass surface density can stabilize the reduced remaining fuel against further star formation. Across all morphologies, galaxies in denser environments show a decreased specific star formation rate from the outside in, supporting an environmental cause for quenching, such as ram-pressure stripping or galaxy interactions.Publisher PDFPeer reviewe
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