469 research outputs found
Probing for evolutionary links between local ULIRGs and QSOs from NIR spectroscopy
We present a study of the dynamical evolution of Ultraluminous Infrared
Galaxies (ULIRGs), merging galaxies of infrared luminosity >10^12 L_sun. During
our Very Large Telescope large program, we have obtained ISAAC near-infrared,
high-resolution spectra of 54 ULIRGs (at several merger phases) and 12 local
Palomar-Green QSOs to investigate whether ULIRGs go through a QSO phase during
their evolution. One possible evolutionary scenario is that after nuclear
coalescence, the black hole radiates close to Eddington to produce QSO
luminosities. The mean stellar velocity dispersion that we measure from our
spectra is similar (~160 km/s) for 30 post-coalescence ULIRGs and 7 IR-bright
QSOs. The black holes in both populations have masses of order 10^7-10^8 M_sun
(calculated from the relation to the host dispersion) and accrete at rates >0.5
Eddington. Placing ULIRGs and IR-bright QSOs on the fundamental plane of
early-type galaxies shows that they are located on a similar region (that of
moderate-mass ellipticals), in contrast to giant ellipticals and radio-loud
QSOs. While this preliminary comparison of the ULIRG and QSO host kinematical
properties indicates that (some) ULIRGs may undergo a QSO phase in their
evolutionary history before they settle down as ellipticals, further data on
non-IR excess QSOs are necessary to test this scenario.Comment: To appear in the "QSO Host Galaxies: Evolution and Environment"
conference proceedings; meeting held in Leiden, August 200
Generation of rotationally dominated galaxies by mergers of pressure-supported progenitors
Through the analysis of a set of numerical simulations of major mergers
between initially non-rotating, pressure supported progenitor galaxies with a
range of central mass concentrations, we have shown that: (1) it is possible to
generate elliptical-like galaxies, with v/sigma > 1 outside one effective
radius, as a result of the conversion of orbital- into internal-angular
momentum; (2) the outer regions acquire part of the angular momentum first; (3)
both the baryonic and the dark matter components of the remnant galaxy acquire
part of the angular momentum, the relative fractions depend on the initial
concentration of the merging galaxies. For this conversion to occur the initial
baryonic component must be sufficiently dense and/or the encounter should take
place on a orbit with high angular momentum. Systems with these hybrid
properties have been recently observed through a combination of stellar
absorption lines and planetary nebulae for kinematic studies of early-type
galaxies. Our results are in qualitative agreement with such observations and
demonstrate that even mergers composed of non-rotating, pressure-supported
progenitor galaxies can produce early-type galaxies with significant rotation
at large radii.Comment: 5 pages, 6 figures, 2 tables. Accepted for publication in A&A Letter
Dynamical properties of Ultraluminous Infrared Galaxies I: Mass ratio conditions for ULIRG activity in interacting pairs
We present first results from our Very Large Telescope large program to study
the dynamical evolution of Ultraluminous Infrared Galaxies (ULIRGs), which are
the products of mergers of gas-rich galaxies. The full data set consists of
high resolution, long-slit, H- and K-band spectra of 38 ULIRGs and 12 QSOs
(between 0.042<z<0.268). In this paper, we present the sources that have not
fully coalesced, and therefore have two distinct nuclei. This sub-sample
consists of 21 ULIRGs, the nuclear separation of which varies between 1.6 and
23.3 kpc. From the CO bandheads that appear in our spectra, we extract the
stellar velocity dispersion, sigma, and the rotational velocity, V_rot. The
stellar dispersion equals 142 km/s on average, while V_rot is often of the same
order. We combine our spectroscopic results with high-resolution infrared (IR)
imaging data to study the conditions for ULIRG activity in interacting pairs.
We find that the majority of ULIRGs are triggered by almost equal-mass major
mergers of 1.5:1 average ratio. Less frequently, 3:1 encounters are also
observed in our sample. However, less violent mergers of mass ratio >3:1
typically do not force enough gas into the center to generate ULIRG
luminosities.Comment: Accepted for publication in "The Astrophysical Journal
Dynamical properties of Ultraluminous Infrared Galaxies. II. Traces of dynamical evolution and end products of local ultraluminous mergers
We present results from our Very Large Telescope large program to study the
dynamical evolution of local Ultraluminous Infrared Galaxies (ULIRGs) and QSOs.
This paper is the second in a series presenting the stellar kinematics of 54
ULIRGs, derived from high resolution, long-slit H- and K-band spectroscopy. The
data presented here, including observations of 17 new targets, are mainly
focused on sources that have coalesced into a single nucleus. The stellar
kinematics, extracted from the CO ro-vibrational bandheads in our spectra,
indicate that ULIRG remnants are dynamically heated systems with a mean
dispersion of 161 km/s. The combination of kinematic, structural, and
photometric properties of the remnants indicate that they mostly originate from
major mergers and that they result in the formation of systems supported by
random motions, therefore, elliptical galaxies. The peak of the velocity
dispersion distribution and the locus of ULIRGs on the fundamental plane of
early-type galaxies indicate that the end products of ultraluminous mergers are
typically moderate-mass ellipticals (of stellar mass ~10^10 - 10^11 M_sun).
Converting the host dispersion into black hole mass with the aid of the
M_BH-sigma relation yields black hole mass estimates of the order 10^7 - 10^8
M_sun and high accretion rates with Eddington efficiencies often >0.5.Comment: Accepted for publication in the Astrophysical Journa
The Milky Way: An Exceptionally Quiet Galaxy; Implications for the formation of spiral galaxies
[Abridged]We compare both the Milky Way and M31 galaxies to local external
disk galaxies within the same mass range, using their relative locations in the
planes formed by V_flat versus M_K, j_disk, and the average Fe abundance of
stars in the galaxy outskirts. We find, for all relationships, that the MW is
systematically offset by ~ 1 sigma, showing a significant deficiency in stellar
mass, in angular momentum, in disk radius and [Fe/H] in the stars in its
outskirts at a given V_flat. On the basis of their location in the M_K, V_flat,
and R_d volume, the fraction of spirals like the MW is 7+/-1%, while M31
appears to be a "typical'' spiral. Our Galaxy appears to have escaped any
significant merger over the last ~10 Gyrs which may explain why it is deficient
by a factor 2 to 3 in stellar mass, angular momentum and outskirts metallicity
and then, unrepresentative of the typical spiral. As with M31, most local
spirals show evidence for a history shaped mainly by relatively recent merging.
We conclude that the standard scenario of secular evolution is generally unable
to reproduce the properties of most (if not all) spiral galaxies. However, the
so-called "spiral rebuilding'' scenario proposed by Hammer et al. 2005 is
consistent with the properties of both distant galaxies and of their
descendants - the local spirals.Comment: 14 pages, 6 figures, to appear in Ap
Towards a resolved Kennicutt-Schmidt law at high redshift
Massive galaxies in the distant Universe form stars at much higher rates than
today. Although direct resolution of the star forming regions of these galaxies
is still a challenge, recent molecular gas observations at the IRAM Plateau de
Bure interferometer enable us to study the star formation efficiency on
subgalactic scales around redshift z = 1.2. We present a method for obtaining
the gas and star formation rate (SFR) surface densities of ensembles of clumps
composing galaxies at this redshift, even though the corresponding scales are
not resolved. This method is based on identifying these structures in
position-velocity diagrams corresponding to slices within the galaxies. We use
unique IRAM observations of the CO(3-2) rotational line and DEEP2 spectra of
four massive star forming distant galaxies - EGS13003805, EGS13004291,
EGS12007881, and EGS13019128 in the AEGIS terminology - to determine the gas
and SFR surface densities of the identifiable ensembles of clumps that
constitute them. The integrated CO line luminosity is assumed to be directly
proportional to the total gas mass, and the SFR is deduced from the [OII] line.
We identify the ensembles of clumps with the angular resolution available in
both CO and [OII] spectroscopy; i.e., 1-1.5". SFR and gas surface densities are
averaged in areas of this size, which is also the thickness of the DEEP2 slits
and of the extracted IRAM slices, and we derive a spatially resolved
Kennicutt-Schmidt (KS) relation on a scale of ~8 kpc. The data generally
indicates an average depletion time of 1.9 Gyr, but with significant variations
from point to point within the galaxies.Comment: 6 pages, 4 figures, 2 tables, accepted by Astronomy and Astrophysic
A Mechanism for the Oxygen and Iron Bimodal Radial Distribution Formation in the Disc of our Galaxy
Recently it has been proposed that there are two types of SN Ia progenitors
-- short-lived and long-lived. On the basis of this idea, we develope a theory
of a unified mechanism for the formation of the bimodal radial distribution of
iron and oxygen in the Galactic disc. The underlying cause for the formation of
the fine structure of the radial abundance pattern is the influence of spiral
arms, specifically, the combined effect of the corotation resonance and
turbulent diffusion. From our modelling we conclude that to explain the bimodal
radial distributions simultaneously for oxygen and iron and to obtain
approximately equal total iron output from different types of supernovae, the
mean ejected iron mass per supernova event should be the same as quoted in
literature if maximum mass of stars, that eject heavy elements, is . For the upper mass limit of the production of iron
by a supernova II explosion should be increased by about 1.5 times.Comment: 7 pages, 6 figures, MNRAS submitte
CANDELS Observations of the Structural Properties and Evolution of Galaxies in a Cluster at z=1.62
We discuss the structural and morphological properties of galaxies in a
z=1.62 proto-cluster using near-IR imaging data from Hubble Space Telescope
Wide Field Camera 3 data of the Cosmic Assembly Near-IR Deep Extragalactic
Legacy Survey (CANDELS). The cluster galaxies exhibit a clear color-morphology
relation: galaxies with colors of quiescent stellar populations generally have
morphologies consistent with spheroids, and galaxies with colors consistent
with ongoing star formation have disk-like and irregular morphologies. The size
distribution of the quiescent cluster galaxies shows a deficit of compact (<
1kpc), massive galaxies compared to CANDELS field galaxies at z=1.6. As a
result the cluster quiescent galaxies have larger average effective sizes
compared to field galaxies at fixed mass at greater than 90% significance.
Combined with data from the literature, the size evolution of quiescent cluster
galaxies is relatively slow from z~1.6 to the present, growing as
(1+z)^(-0.6+/-0.1). If this result is generalizable, then it implies that
physical processes associated with the denser cluster region seems to have
caused accelerated size growth in quiescent galaxies prior to z=1.6 and slower
subsequent growth at z<1.6 compared to galaxies in the lower density field. The
quiescent cluster galaxies at z=1.6 have higher ellipticities compared to lower
redshift samples at fixed mass, and their surface-brightness profiles suggest
that they contain extended stellar disks. We argue the cluster galaxies require
dissipationless (i.e., gas-poor or "dry") mergers to reorganize the disk
material and to match the relations for ellipticity, stellar mass, size, and
color of early-type galaxies in z<1 clusters.Comment: Accepted for publication in ApJ. 14 pages in emulateapj format.
Replacement includes improvements from referee report, and updates and
additions to reference
PHIBSS: molecular gas content and scaling relations in z~1-3 normal star forming galaxies
We present PHIBSS, the IRAM Plateau de Bure high-z blue sequence CO 3-2
survey of the molecular gas properties in normal star forming galaxies (SFGs)
near the cosmic star formation peak. PHIBSS provides 52 CO detections in two
redshift slices at z~1.2 and 2.2, with log(M*(M_solar))>10.4 and
log(SFR(M_solar/yr))>1.5. Including a correction for the incomplete coverage of
the M*-SFR plane, we infer average gas fractions of ~0.33 at z~1.2 and ~0.47 at
z~2.2. Gas fractions drop with stellar mass, in agreement with cosmological
simulations including strong star formation feedback. Most of the z~1-3 SFGs
are rotationally supported turbulent disks. The sizes of CO and UV/optical
emission are comparable. The molecular gas - star formation relation for the
z=1-3 SFGs is near-linear, with a ~0.7 Gyrs gas depletion timescale; changes in
depletion time are only a secondary effect. Since this timescale is much less
than the Hubble time in all SFGs between z~0 and 2, fresh gas must be supplied
with a fairly high duty cycle over several billion years. At given z and M*,
gas fractions correlate strongly with the specific star formation rate. The
variation of specific star formation rate between z~0 and 3 is mainly
controlled by the fraction of baryonic mass that resides in cold gas.Comment: Submitted to the Astrophysical Journal; 14 figure
Adaptive optics imaging and optical spectroscopy of a multiple merger in a luminous infrared galaxy
(abridged) We present near-infrared (NIR) adaptive optics imaging obtained
with VLT/NACO and optical spectroscopy from the Southern African Large
Telescope (SALT) of a luminous infrared galaxy (LIRG) IRAS 19115-2124. These
data are combined with archival HST imaging and Spitzer imaging and
spectroscopy, allowing us to study this disturbed interacting/merging galaxy,
dubbed the Bird, in extraordinary detail. In particular, the data reveal a
triple system where the LIRG phenomenon is dominated by the smallest of the
components.
One nucleus is a regular barred spiral with significant rotation, while
another is highly disturbed with a surface brightness distribution intermediate
to that of disk and bulge systems, and hints of remaining arm/bar structure. We
derive dynamical masses in the range 3-7x10^10 M_solar for both. The third
component appears to be a 1-2x10^10 M_solar mass irregular galaxy. The total
system exhibits HII galaxy-like optical line ratios and strengths, and no
evidence for AGN activity is found from optical or mid-infrared data. The star
formation rate is estimated to be 190 M_solar/yr. We search for SNe, super star
clusters, and detect 100-300 km/s outflowing gas from the Bird. Overall, the
Bird shows kinematic, dynamical, and emission line properties typical for cool
ultra luminous IR galaxies. However, the interesting features setting it apart
for future studies are its triple merger nature, and the location of its star
formation peak - the strongest star formation does not come from the two major
K-band nuclei, but from the third irregular component. Aided by simulations, we
discuss scenarios where the irregular component is on its first high-speed
encounter with the more massive components.Comment: 24 pages, 16 figures. Accepted MNRAS version, minor corrections only,
references added. Higher resolution version (1.3MB) is available from
http://www.saao.ac.za/~petri/bird/ulirg_bird_highres_vaisanen_v2.pd
- …