24 research outputs found
The Montreal Blue Galaxy Survey III. Third list of UV-bright candidates
We present and discuss the latest addition of the Montreal Blue Galaxy (MBG)
survey. Inspection of 59 Curtis Schmidt plates resulted in the identification
of 135 new UV-bright galaxies with B < 15.5. This brings the total number of
MBGs to 469. New results of the test show that our survey is complete
to B = 14.7.
From our most recent spectroscopic follow-up, we confirm the discovery of one
new Seyfert 1 galaxy and possibly one new Seyfert 2 galaxy. We confirm also the
bias of the MBG survey towards the low-excitation and metal rich Starburst
Nucleus Galaxies (SBNGs). The spectral characteristics of the MBGs are similar
to those of the infrared luminous IRAS galaxies. As a common characteristic,
they show a mean ratio Log([NII]/H) in excess of 0.2 dex as compared to
normal disk HII regions. In general, the MBGs have lower far-infrared
luminosities () and are nearer (z < 0.05) than the
luminous IRAS galaxies.
The distribution of the morphologies of the MBGs indicates a high number of
early-type spirals (Sb and earlier). Nearly half of these galaxies also possess
a bar. In our sample, the fraction of galaxies with bars depends on the
morphology and increases towards the late-type spirals. However, if we consider
only isolated galaxies, the late-type spirals show a clear tendency to be
barred. Signs of a recent interaction with neighbor galaxies are obvious only
in 24% of our candidates. Although this number is only a lower limit, it is
nevertheless sufficiently low to suggest that in a majority of massive galaxies
the burst of star formation do not depends solely on dynamical processes.Comment: 24 pages, 6 Latex tables and 6 Postscript figures, uses aasms4.sty,
accepted for publication in the Astronomical journa
Relation between Brown Dwarfs and Exoplanets
One of the most debated subjects in Astronomy since the discovery of
exoplanets is how can we distinguish the most massive of such objects from
very-low mass stars like Brown Dwarfs (BDs)? We have been looking for evidences
of a difference in physical characteristics that could be related to different
formation processes. Using a new diagnostic diagram that compares the baryonic
gravitational potential (BGP) with the distances from their host stars, we have
classified a sample of 355 well-studied exoplanets according to their possible
structures. We have then compared the exoplanets to a sample of 87 confirmed
BDs, identifying a range in BGP that could be common to both objects. By
analyzing the mass-radius relations (MRR) of the exoplanets and BDs in those
different BGP ranges, we were able to distinguish different characteristic
behaviors. By comparing with models in the literature, our results suggest that
BDs and massive exoplanets might have similar structures dominated by liquid
metallic hydrogen (LMH).Comment: Poster #149 from proceeding of The 19th Cambridge Workshop on Cool
Stars, Stellar Systems, and the Sun; 06-10 June 2016, Uppsala, Swede
Probing the rapid formation of black holes and their galaxy hosts in QSOs
Using the modelling code X-CIGALE, we reproduced the SEDs of 1,359 SDSS QSOs
within the redshift range 0 < z < 4, for which we have NIR/MIR fluxes with the
highest quality and spectral data characterizing their SMBHs. Consistent with a
rapid formation of the host galaxies, the star formation histories (SFHs) have
small e-folding, at most 750 Myrs using an SFH function for Spiral or 1000 Myrs
using one for Elliptical. Above z \sim 1.6, the two solutions are degenerate,
the SEDs being dominated by the AGN continuum and high star formation rates
(SFRs), typical of starburst galaxies, while at lower redshifts the starburst
nature of the host, independent from its morphology, is better reproduced by an
Spiral SFH. In general, the SFR increases with the redshift, the mass of the
bulge, the AGN luminosity and Eddington ratio, suggesting there is no evidence
of AGN quenching of star formation. Comparing the specific BHAR with specific
SFR, all the QSOs at any redshift trace a linear sequence below the Eddington
luminosity, in parallel and above the one-to-one relation, implying that QSOs
are in a special phase of evolution during which the growth in mass of their
SMBH is more rapid than the growth in mass of their galaxy hosts. This
particular phase is consistent with a scenario where the galaxy hosts of QSOs
in the past grew in mass more rapidly than their SMBHs, suggesting that a high
star formation efficiency during their formation was responsible in limiting
their massesComment: Accepted in MNRAS 2023 February 28. Received 2023 February 28; in
original form 2022 July 0
The Relation Between Activity and Environment in Compact Groups of Galaxies
We present the results of the classification of spectral activity types for
193 galaxies from a new sample of 49 compact groups of galaxies in the southern
hemisphere (SCGs). This sample was selected in automated fashion from a
digitized galaxy catalogue, covering an area of ~5200 sq deg, around the South
Galactic Pole. It is complete up to m ~14.5 in b_j for the brightest galaxy of
the group.
The spectral analysis of the SCG galaxies confirms the results previously
obtained for a smaller sample of Hickson's compact groups (HCG). We confirm the
luminosity-activity and morphology-activity relations, as well as the
predominance of AGNs (41% of SCGs galaxies). We verified also that the number
of early-type non-emission-line galaxies increases with the number of members
in the group.
The SCGs contain more star-forming galaxies (SFGs) and less non-emission-line
galaxies than HCGs, which suggests that they probe a wider range of physical
properties. The SFGs are composed in majority of HII Nucleus Galaxies, which
have less intense star formation than starburst galaxies. The star formation
activity in SCGs is, consequently, remarkably low. The SFGs show also evidence
for nuclear activity. If these results are further confirmed, 70% of the
galaxies in SCGs would then have an active nucleus, making these systems
remarkably rich in AGNs. Curiously, however, this characteristic of CGs
generally excludes Seyfert 1 galaxies.(Abridged)Comment: 53 pages, Latex, 9 encapsulated postscript figures, Accepted for
publication in The Astronomical Journa
The Nature of the Activity in Hickson Compact Groups of Galaxies
We present the results of the spectral classification of the 82 brightest
galaxies in a sample of 17 compact groups. We verify that the AGNs are
preferentially located in the most early-type and luminous galaxies of the
groups, as is usually observed in the field. But these AGNs also appear to be
systematically concentrated towards the central parts of the groups. Our
observations suggest a correlation between activity types, morphologies and
densities of galaxies in the compact groups. This is consistent with a scenario
in which galaxies of compact groups evolve by interacting with their
environment and are currently in a quiet phase of their activityComment: 22 pages, LaTeX (aasms4.sty) + 7 figures; accepted for publication in
the Astrophysical Journa
HCG 16 Revisited: Clues About Galaxy Evolution in Groups
We present new spectroscopic observations of 5 galaxies, members of the
unusually active compact group HCG 16, observed using the Palomar 5m telescope.
The high signal to noise ratios (S/N ) of the spectra allow us to
study the variation of the emission line characteristics and the stellar
populations in the nucleus and the circumnuclear regions of the galaxies. The
emission line characteristics of these galaxies are complex, varying between
Seyfert 2 and LINERs or between LINERs and starbursts. All of the galaxies show
traces of intermediate age stellar populations, supporting our previous result
that post-starburst galaxies are common in compact groups. The galaxies
HCG16--4 and HCG16--5 show double nuclei and therefore could be two cases of
recent merger. Our observations support a scenario where HCG 16 was formed by
the successive merger of metal poor, low mass galaxies. The galaxies HCG16--1
and HCG16--2, which are more evolved, form the old core of the group. Galaxies
HCG16--4 and HCG16--5 are two more recent additions still in a merging phase.
Galaxy HCG16--5 is a starburst galaxy which is just beginning to fall into the
core. If HCG 16 is representative of compact groups in their early stage, the
whole set of observations implies that the formation of compact groups is the
result of hierarchical galaxy formation. HCG 16 could be one example of this
process operating in the local universe.Comment: tar file containing text and figures is available at
http://www.daf.on.br/~reinaldo/paper.htm
Discovery of a Luminous Quasar in the Nearby Universe
In the course of the Pico dos Dias survey (PDS), we identified the stellar
like object PDS456 at coordinates alpha = 17h 28m 19.796s, delta = -14deg 15'
55.87'' (epoch 2000), with a relatively nearby (z = 0.184) and bright (B =
14.69) quasar. Its position at Galactic coordinates l_II = 10.4deg, b_II =
+11.2deg, near the bulge of the Galaxy, may explain why it was not detected
before. The optical spectrum of PDS456 is typical of a luminous quasar, showing
a broad (FWHM ~ 4000 km/s) H_\beta line, very intense FeII lines and a weak
[OIII]\lambda5007 line. PDS456 is associated to the infrared source IRAS
17254-1413 with a 60 \mum infrared luminosity L_{60} = 3.8 x 10^{45} erg/s. The
relatively flat slopes in the infrared (\alpha(25,60) = -0.33 and \alpha(12,25)
= -0.78) and a flat power index in the optical (F_{\nu} \propto \nu^{-0.72})
may indicate a low dust content. A good match between the position of PDS456
and the position of the X-ray source RXS J172819.3-141600 implies an X-ray
luminosity L_x = 2.8 x 10^{44} erg/s. The good correlation between the strength
of the emission lines in the optical and the X-ray luminosity, as well as the
steep optical to X-ray index estimated (\alpha_{ox} = -1.64) suggest that
PDS456 is radio quiet. A radio survey previously performed in this region
yields an upper limit for radio power at ~ 5 GHz of ~ 2.6 x 10^{30} erg/s/Hz.
We estimate the Galactic reddening in this line-of-sight to be A_B \simeq 2.0,
implying an absolute magnitude M_B = -26.7 (using H_0 = 75 km s^{-1} Mpc^{-1}
and q_0 = 0). In the optical, PDS456 is therefore 1.3 times more luminous than
3C 273 and the most luminous quasar in the nearby (z \leq 0.3) Universe.Comment: 12 pages, LaTeX (aasms4.sty) + 3 figures; accepted for publication in
the Astrophysical Journal Letter