3 research outputs found
Near-infrared imaging and spectroscopy of the nuclear region of the disturbed Virgo cluster spiral NGC 4438
We present near-infrared VLT ISAAC imaging and spectroscopy of the peculiar
Virgo galaxy NGC 4438, whose nucleus has been classified as a LINER. The data
are supplemented by mid-infrared imaging, and compared to previous WFPC2 HST
broadband images. Images and position-velocity maps of the [Fe II] and H2 line
emissions are presented and compared with the distribution of the optical
narrow-line region and radio features. Our results show that shocks (possibly
driven by a radio jet) contribute to an important fraction of the excitation of
[Fe II], while X-ray heating from a central AGN may be responsible for the H2
excitation. We address the question whether the outflow has an AGN or a
starburst origin by providing new estimates of the central star formation rate
and the kinetic energy associated with the gas. By fitting a Sersic bulge, an
exponential disc and a compact nuclear source to the light distribution, we
decomposed NGC 4438's light distribution and found an unresolved nuclear source
at 0.8 arcsec resolution with M_K = -18.7 and J-H = 0.69. Our measured bulge
velocity dispersion, 142 km/s, together with the standard M_bh-sigma relation,
suggests a central black hole mass of log(M_bh/Msun) ~ 7.0. The stellar
kinematics measured from the near-infrared CO lines shows a strong peak in the
velocity dispersion of 178 km/s in the central 0.5 arcsec, which is possible
kinematic evidence of a central black hole. We calculated a general expression
for the integrated Sersic profile flux density in elliptical geometry,
including the case of 'disky' isophotes.Comment: 13 pages, 12 figures. Affiliation added. Higher resolution image
2MASS photometry of edge-on spiral galaxies. I. Sample and general results
A sample of edge-on spiral galaxies aimed at a study of the main structural
and photometric parameters of edge-on galaxies both of early and late types is
presented. The data were taken from the 2MASS in the J, H and K_s filters. The
sample consists of 175 galaxies in the K_s-filter, 169 galaxies in the H-filter
and 165 galaxies in the J-filter. We present bulge and disc decompositions of
each galaxy image. All galaxies have been modelled with a Sersic bulge and
exponential disc with the BUDDA v2.1 package.
The main conclusions of our general statistical analysis of the sample are:
(1) The distribution of the apparent bulge axis ratio q_b for the subsample
with n < 2 can be attributed to triaxial, nearly prolate bulges that are seen
from different projections, while n > 2 bulges seem to be oblate spheroids with
moderate flattening.
(2) For the sample galaxies, the effective radius of the bulge r_{e,b}, the
disc scalelength h and the disc scaleheight z_0 are well correlated. However,
there is a clear trend for the ratio r_{e,b}/h to increase with n.
(3) There is a hint that the fundamental planes of discs, which links only
disc parameters and the maximum rotational velocity of gas, are different for
galaxies with different bulges.
(4) The investigation of the Photometric Plane of sample bulges shows that
the plane is not flat and has a prominent curvature towards small values of n.
For bulges this fact was not noticed earlier.
(5) The clear relation between the flattening of stellar discs h/z_0 and the
relative mass of a spherical component, including a dark halo, is confirmed not
for bulgeless galaxies but for galaxies with massive bulges. (Abridged)Comment: 20 pages, 13 figures, accepted for publication in MNRA
High-redshift elliptical galaxies: are they (all) really compact?
We investigate the properties of 12 ultra-massive passively evolving early
type galaxies (ETGs) at z_phot>1.4 in the COSMOS 2 deg^2 field. These 12 ETGs
were selected as pBzKs, have accurate 1.4<= z_phot <=1.7,high Sersic index
profiles typical of ellipticals, no detection at 24 micron, resulting in a
complete ETG sample at M*>2.5x10^11 M_sun (Chabrier IMF). Contrary to previous
claims, the half light radii estimated in very high S/N imaging data from
HST+ACS are found to be large for most of the sample, consistent with local
ellipticals. If the high redshift ETGs with M*<2.5x10^11 M_sun are really small
in size and compact as reported in previous studies, our result may suggest a
"downsizing" scenario, whereby the most massive ETGs reach their final
structure earlier and faster than lower mass ones. However, simulating galaxies
with morphological properties fixed to those of local ETGs with the same
stellar mass show that the few compact galaxies that we still recover in our
sample can be understood in term of fluctuations due to noise preventing the
recovery of the extended low surface brightness halos in the light profile.
Such halos, typical of Sersic profiles, extending even up to 40 kpc, are indeed
seen in our sample.Comment: 9 pages, 7 figures, accepted by MNRA