157 research outputs found
Red-channel (6000-8000 {\AA}) nuclear spectra of 376 local galaxies
We obtained long-slit optical spectra of the nuclear regions of 376 galaxies
in the local Universe using the 1.5m Cassini telescope of Bologna Observatory.
Of these spectra, 164 were either never taken before by the Sloan Digital Sky
Survey (SDSS), or given by the Nasa Extragalactic Database (NED). With these
new spectra, we contribute investigating the occurrence of active galactic
nuclei (AGNs). Nevertheless, we stress that the present sample is by no means
complete, thus, it cannot be used to perform any demographic study. Following
the method presented in Gavazzi et al. (2011), we classify the nuclear spectra
using a six bin scheme: SEY (Seyfert), sAGN (strong AGN), and wAGN (weak AGN)
represent active galactic nuclei of different levels of activity; HII accounts
for star-forming nuclei; RET (retired) and PAS (passive) refer to nuclei with
poor or no star-formation activity. The spectral classification is performed
using the ratio of 6584 {\lambda} [NII] to H{\alpha} lines and the equivalent
width (EW) of H{\alpha} versus [NII]/H{\alpha} (WHAN diagnostic introduced by
Cid Fernandes and collaborators) after correcting H{\alpha} for underlying
absorption. The obtained spectra are made available in machine readable format
via the Strasbourg Astronomical Data Center (CDS) and NED.Comment: 8 pages, 6 Figures, 4 Tables, accepted for publication in Astronomy &
Astrophysic
A complete spectroscopic catalogue of local galaxies in the Northern spring sky -- Gas properties and nuclear activity in different environments
With the aim of providing the complete demography of galaxies in the local
Universe, including their nuclear properties, we present SPRING, a complete
census of local galaxies limited to the spring quarter of the Northern sky
(10h< RA <16h; 0< Dec <65). The SPRING catalogue is a flux- and volume-limited
sample (r < 17.7 mag, cz < 10000 km/s) of 30597 galaxies, including the Virgo,
Coma and A1367 clusters. To inspect possible secular and environmental
dependencies of the various nuclear excitation properties (SF vs. AGN), we
perform a multidimensional analysis by dividing the sample according to (i)
their position in the (NUV-i) vs. M* diagram,(ii) local galaxy density, (iii)
stellar-mass, (iv) halo-mass of the group to which galaxies belong, and (v)
neutral Hydrogen content. We present a new calibration of the optical
diameter-based HI-deficiency parameter employing a reference sample of isolated
galaxies. At intermediate distances between Virgo and Coma, we identify a
ring-like structure of galaxies constituted by three large filaments. The
fraction of HI-deficient galaxies within the filament suggests that filaments
are a transitioning environment between field and cluster in terms of HI
content. We classify the nuclear spectra according to the four-line BPT and the
two-line WHAN diagrams, and investigate the variation in the fraction of AGN
with stellar-mass, as well as their colours and environments. In general, we
observe that the mass-dependency of the fraction of Seyfert nuclei is little
sensitive to the environment, whereas the fraction of star-forming nuclei is a
steeper function of M* in lower-density environments and in blue-cloud
galaxies. We find that the fraction of LINERs depends on galaxy colour and, for
logM* > 9.5-10, increases in galaxies belonging to the green valley.Comment: 26 pages, 22 figures. Accepted for publication in Astronomy &
Astrophysic
On the influence of environment on star forming galaxies
We use our state-of-the-art semi analytic model for GAlaxy Evolution and
Assembly (GAEA), and observational measurements of nearby galaxies to study the
influence of the environment on the gas content and gaseous/stellar disc sizes
of star-forming galaxies. We analyse the origin of differences between physical
properties of satellites and those of their central counterparts, identified by
matching the Vmax of their host haloes at the accretion time of the satellites.
Our model reproduces nicely the differences between centrals and satellites
measured for the HI mass, size of the star-forming region, and stellar radii.
In contrast, our model predicts larger differences with respect to data for the
molecular gas mass and star formation rate. By analysing the progenitors of
central and satellite model galaxies, we find that differences in the gas
content arise after accretion, and can be entirely ascribed to the
instantaneous stripping of the hot gas reservoir. The suppression of cold gas
replenishment via cooling and star formation leads to a reduction of the cold
gas and of its density. Therefore, more molecular gas is lost than lower
density HI gas, and model satellites have less molecular gas and lower star
formation rates than observed satellites. We argue that these disagreements
could be largely resolved with the inclusion of a proper treatment for
ram-pressure stripping of cold gas and a more gradual stripping of the hot gas
reservoir. A more sophisticated treatment of angular momentum exchanges,
accounting for the multi-phase nature of the gaseous disc is also required.Comment: 15 pages, 9 figures, accepted for publication in MNRA
Turbulence in the Tail of a Jellyfish Galaxy
When galaxies move through the intracluster medium (ICM) inside galaxy
clusters, the ram pressure of the ICM can strip the gas from galaxies. The
stripped gas forms tails on the trailing side. These galaxies are hence dubbed
``jellyfish galaxies''. ESO 137-001 is a quintessential jellyfish galaxy
located in the nearest rich cluster, the Norma cluster. Its spectacular
multiphase tail has complex morphology and kinematics both from the imprinted
galaxy's interstellar medium (ISM) and as a result of the interactions between
the stripped gas and the surrounding hot plasma, mediated by radiative cooling
and magnetic fields. We study the kinematics of the multiphase tail using
high-resolution observations of the ionized and the molecular gas in the entire
structure. We calculate the velocity structure functions (VSFs) in moving
frames along the tail and find that turbulence driven by Kelvin-Helmholtz (KH)
instability quickly overwhelms the original ISM turbulence and saturates at
kpc. There is also a hint that the far end of the tail has possibly
started to inherit pre-existing large-scale ICM turbulence likely caused by
structure formation. Turbulence measured by the molecular gas is generally
consistent with that measured by the ionized gas in the tail but has a slightly
lower amplitude. Most of the measured turbulence is below the mean free path of
the hot ICM ( kpc). Using warm/cool gas as a tracer of the hot ICM, we
find that the isotropic viscosity of the hot plasma must be suppressed below
0.01 percent Spitzer level.Comment: 7 pages, 6 figures, accepted for publication in MNRA
SRGAP2 and Its Human-Specific Paralog Co-Regulate the Development of Excitatory and Inhibitory Synapses.
The proper function of neural circuits requires spatially and temporally balanced development of excitatory and inhibitory synapses. However, the molecular mechanisms coordinating excitatory and inhibitory synaptogenesis remain unknown. Here we demonstrate that SRGAP2A and its human-specific paralog SRGAP2C co-regulate the development of excitatory and inhibitory synapses in cortical pyramidal neurons in vivo. SRGAP2A promotes synaptic maturation, and ultimately the synaptic accumulation of AMPA and GABAA receptors, by interacting with key components of both excitatory and inhibitory postsynaptic scaffolds, Homer and Gephyrin. Furthermore, SRGAP2A limits the density of both types of synapses via its Rac1-GAP activity. SRGAP2C inhibits all identified functions of SRGAP2A, protracting the maturation and increasing the density of excitatory and inhibitory synapses. Our results uncover a molecular mechanism coordinating critical features of synaptic development and suggest that human-specific duplication of SRGAP2 might have contributed to the emergence of unique traits of human neurons while preserving the excitation/inhibition balance
MUSE Analysis of Gas around Galaxies (MAGG) -- V: Linking ionized gas traced by CIV and SiIV absorbers to Ly emitting galaxies at
We use 28 quasar fields with high-resolution (HIRES and UVES) spectroscopy
from the MUSE Analysis of Gas Around Galaxies survey to study the connection
between Ly emitters (LAEs) and metal-enriched ionized gas traced by
CIV in absorption at redshift . In a sample of 220 CIV absorbers,
we identify 143 LAEs connected to CIV gas within a line-of-sight separation
, equal to a detection rate of per cent
once we account for multiple LAEs connected to the same CIV absorber. The
luminosity function of LAEs associated with CIV absorbers shows a
higher normalization factor compared to the field. CIV with higher equivalent
width and velocity width are associated with brighter LAEs or multiple
galaxies, while weaker systems are less often identified near LAEs. The
covering fraction in groups is up to times larger than for isolated
galaxies. Compared to the correlation between optically-thick HI absorbers and
LAEs, CIV systems are twice less likely to be found near LAEs especially at
lower equivalent width. Similar results are found using SiIV as tracer of
ionized gas. We propose three components to model the gas environment of LAEs:
i) the circumgalactic medium of galaxies, accounting for the strongest
correlations between absorption and emission; ii) overdense gas filaments
connecting galaxies, driving the excess of LAEs at a few times the virial
radius and the modulation of the luminosity and cross-correlation functions for
strong absorbers; iii) an enriched and more diffuse medium, accounting for
weaker CIV absorbers farther from galaxies.Comment: 28 pages, 21 figures, 10 tables. Submitted to MNRAS after accounting
for reviewer's comment
The definition of environment and its relation to the quenching of galaxies at z=1-2 in a hierarchical Universe
A well calibrated method to describe the environment of galaxies at all
redshifts is essential for the study of structure formation. Such a calibration
should include well understood correlations with halo mass, and the possibility
to identify galaxies which dominate their potential well (centrals), and their
satellites. Focusing on z = 1 and 2 we propose a method of environmental
calibration which can be applied to the next generation of low to medium
resolution spectroscopic surveys. Using an up-to-date semi-analytic model of
galaxy formation, we measure the local density of galaxies in fixed apertures
on different scales. There is a clear correlation of density with halo mass for
satellite galaxies, while a significant population of low mass centrals is
found at high densities in the neighbourhood of massive haloes. In this case
the density simply traces the mass of the most massive halo within the
aperture. To identify central and satellite galaxies, we apply an
observationally motivated stellar mass rank method which is both highly pure
and complete, especially in the more massive haloes where such a division is
most meaningful. Finally we examine a test case for the recovery of
environmental trends: the passive fraction of galaxies and its dependence on
stellar and halo mass for centrals and satellites. With careful calibration,
observationally defined quantities do a good job of recovering known trends in
the model. This result stands even with reduced redshift accuracy, provided the
sample is deep enough to preserve a wide dynamic range of density.Comment: 19 pages, 12 figures, accepted for publication in MNRA
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