37 research outputs found
A multi-particle model of the 3C 48 host
The first successful multi-particle model for the host of the well-known
quasi-stellar object (QSO) 3C 48 is reported. It shows that the morphology and
the stellar velocity field of the 3C 48 host can be reproduced by the merger of
two disk galaxies. The conditions of the interaction are similar to those used
for interpreting the appearance of the ''Antennae'' (NGC 4038/39) but seen from
a different viewing angle. The model supports the controversial hypothesis that
3C 48A is the second nucleus of a merging galaxy, and it suggests a simple
solution for the problem of the missing counter tidal tail.Comment: 5 pages, 5 figures, accepted for publication in A&
High-redshift QSOs in the GOODS
The Great Observatories Origins Deep Survey provides significant constraints
on the space density of less luminous QSOs at high redshift, which is
particularly important to understand the interplay between the formation of
galaxies and super-massive black holes and to measure the QSO contribution to
the UV ionizing background. We present the results of a search for high-z QSOs,
identified in the two GOODS fields on the basis of deep imaging in the optical
(with HST) and X-ray (Chandra), and discuss the allowed space density of QSOs
in the early universe.Comment: Proceedings of 'Multiwavelength mapping of galaxy evolution'
conference held in Venice (Italy), October 2003, A. Renzini and R. Bender
(Eds.), 6 pages, 1 figur
Evolution of Disk Galaxies in the GOODS-South Field: Number Densities and Size Distribution
We examine the evolution of the sizes and number densities of disk galaxies
using the high resolution images obtained by the Great Observatories Origins
Deep Survey (GOODS) with the Advanced Camera for Surveys (ACS) on the Hubble
Space Telescope (HST). The multiwavelength (B,V,i,z) images allow us to
classify galaxies based on their rest-frame B-band morphologies out to redshift
z = 1.25. In order to minimize the effect of selection biases, we confine our
analysis to galaxies which occupy the region of magnitude-size plane where the
survey is almost 90% complete at all redshifts. The observed size distribution
is consistent with a log-normal distribution as seen for the disk galaxies in
the local Universe and does not show any significant evolution over the
redshift range 0.25 < z < 1.25. We find that the number densities of disk
galaxies remains fairly constant over this redshift range, although a modest
evolution by a factor of four may be possible within the 2-sigma uncertainties.Comment: accepted for publication in ApJL, 4 page
Hubble Space Telescope Ultraviolet Spectroscopy of Fourteen Low-Redshift Quasars
We present low-resolution ultraviolet spectra of 14 low redshift (z<0.8)
quasars observed with HST/STIS as part of a Snap project to understand the
relationship between quasar outflows and luminosity. By design, all
observations cover the CIV emission line. Nine of the quasars are from the
Hamburg-ESO catalog, three are from the Palomar-Green catalog, and one is from
the Parkes catalog. The sample contains a few interesting quasars including two
broad absorption line (BAL) quasars (HE0143-3535, HE0436-2614), one quasar with
a mini-BAL (HE1105-0746), and one quasar with associated narrow absorption
(HE0409-5004). These BAL quasars are among the brightest known (though not the
most luminous) since they lie at z<0.8. We compare the properties of these BAL
quasars to the z1.4 Large Bright Quasar samples. By
design, our objects sample luminosities in between these two surveys, and our
four absorbed objects are consistent with the v ~ L^0.62 relation derived by
Laor & Brandt (2002). Another quasar, HE0441-2826, contains extremely weak
emission lines and our spectrum is consistent with a simple power-law
continuum. The quasar is radio-loud, but has a steep spectral index and a
lobe-dominated morphology, which argues against it being a blazar. The unusual
spectrum of this quasar resembles the spectra of the quasars PG1407+265,
SDSSJ1136+0242, and PKS1004+13 for which several possible explanations have
been entertained.Comment: Uses aastex.cls, 21 pages in preprint mode, including 6 figures and 2
tables; accepted for publication in The Astronomical Journal (projected vol
133
HI absorption towards nearby compact radio sources
We present the results of HI absorption measurements towards a sample of
nearby Compact Steep-Spectrum (CSS) and Giga-Hertz Peaked Spectrum (GPS) radio
sources, the CORALZ sample, using the Giant Metrewave Radio Telescope (GMRT).
We observed a sample of 18 sources and find 7 new detections. These sources are
of lower luminosity than earlier studies of CSS and GPS objects and we
investigate any dependence of HI absorption features on radio luminosity.
Within the uncertainties, the detection rates and column densities are similar
to the more luminous objects, with the GPS objects exhibiting a higher
detection rate than for the CSS objects. The relative velocity of the
blueshifted absorption features, which may be due to jet-cloud interactions,
are within 250 km s and do not appear to extend to values over
1000 km s seen for the more luminous objects. This could be due to the
weaker jets in these objects, but requires confirmation from observations of a
larger sample of sources. There appears to be no evidence of any dependence of
HI column density on either luminosity or redshift, but these new detections
are consistent with the inverse relation between HI column density and
projected linear size.Comment: 10 pages, 6 figures, accepted for publication in MNRA
New photometric and spectroscopic observations of the Seyfert galaxy Mrk 315
We present new important results about the intermediate-type Seyfert galaxy
Mrk 315, recently observed through optical imaging and integral-field
spectroscopy. Broad-band images were used to study the morphology of the host
galaxy, narrow-band H-alpha images to trace the star forming regions, and
middle-band [O III] images to evidence the distribution of the highly ionised
gas. Some extended emission regions were isolated and their physical properties
studied by means of flux calibrated spectra. High resolution spectroscopy was
used to separate different kinematic components in the velocity fields of gas
and stars. Some peculiar features characterise this apparently undisturbed and
moderately isolated active galaxy. Such features, already investigated by other
authors, are re-analysed and discussed in the light of these new observations.
The most relevant results we obtained are: the multi-tiers structure of the
disc; the presence of a quasi-ring of regions with star formation much higher
than previous claims; a secondary nucleus confirmed by a stellar component
kinematically decoupled by the main galaxy; a new hypothesis about the
controversial nature of the long filament, initially described as hook-shaped,
and more likely made of two independent filaments caused by interaction events
between the main galaxy and two dwarf companions.Comment: 14 pages, 16 figures (7 figures in jpeg format), accepted for
publication in MNRA
Multi-wavelength Study of IRAS 19254-7245 - The Superantennae
We present observations in the optical, near-infrared and millimetre bands of
the Ultraluminous Infrared galaxy IRAS 19254-7245, also known as "The
Superantennae". This galaxy is an interacting system with a double nucleus and
long tails extending for about 350 kpc. We studied in detail the southern
component of the system which is optically classified as a Sy2 galaxy. We have
developed a method to determine the parameters of the emission lines in a
spectrum in the case of multiple components and severe blending. Our data allow
us to build a picture of the environment around the nucleus of the galaxy with
unprecedented detail. The optical lines show a complex dynamical structure that
is not observable in the near-infrared. In addition we find typical features of
AGN such as the coronal lines of [FeVII]5721 and [SiVI]1.96. We also detect
strong emission from [FeII]1.64 and
Probing radio source environments via HI and OH absorption
We present the results of HI and OH absorption measurements towards a sample
of radio sources using the Arecibo 305-m telescope and the GMRT. In total, 27
radio sources were searched for associated 21-cm HI absorption. One totally new
HI absorption system was detected against the radio galaxy 3C258, while five
previously known HI absorption systems, and one galaxy detected in emission,
were studied with improved frequency resolution and/or sensitivity. Our sample
included 17 GPS and CSS objects, 4 of which exhibit HI absorption. This
detection rate of ~25% compares with a value of ~40% by Vermeulen et al. for
similar sources. We detected neither OH emission nor absorption towards any of
the sources that were observed at Arecibo, and estimate a limit on the
abundance ratio of N(HI)/N(OH)>4x10^6 for 3C258. We have combined our results
with those from other available HI searches to compile a heterogeneous sample
of 96 radio sources consisting of 27 GPS, 35 CSS, 13 flat spectrum and 21 large
sources. The HI absorption detection rate is highest (~45%) for the GPS sources
and least for the large sources. We find HI column density to be anticorrelated
with source size, as reported earlier by Pihlstr\"om et al. The HI column
density shows no significant dependence on either redshift or luminosity, which
are themselves strongly correlated. These results suggest that the environments
of radio sources on GPS/CSS scales are similar at different redshifts. Further,
in accordance with the unification scheme, the GPS/CSS galaxies have an HI
detection rate of ~40% which is significantly higher than the detection rate
(~20%) towards the GPS/CSS quasars. Also, the principal (strongest) absorption
component detected towards GPS sources appears blue-shifted in ~65% of the
cases, in agreement with the growing evidence for jet-cloud interactions.Comment: Abridged abstract, 22 pages, 21 figures, moderately revised, accepted
for publication in MNRA