18 research outputs found
Testing the presence of multiple photometric components in nearby early-type galaxies using SDSS
We investigate two-dimensional image decomposition of nearby, morphologically
selected early-type galaxies (ETGs). We are motivated by recent observational
evidence of significant size growth of quiescent galaxies and theoretical
development advocating a two-phase formation scenario for ETGs. We find that a
significant fraction of nearby ETGs show changes in isophotal shape that
require multi-component models. The characteristic sizes of the inner and outer
component are and kpc. The inner component lies on the
mass-size relation of ETGs at , while the outer component
tends to be more elliptical and hints at a stochastic buildup process. We find
real physical differences between the single- and double-component ETGs, with
the double-component galaxies being younger and more metal-rich. The fraction
of double component ETGs increases with increasing and decreases in
denser environments. We hypothesize that double-component systems were able to
accrete gas and small galaxies until later times, boosting their central
densities, building up their outer parts, and lowering their typical central
ages. In contrast, the oldest galaxies, perhaps due to residing in richer
environments, have no remaining hints of their last accretion episode.Comment: resubmitted to ApJ after referee's repor
The extended narrow-line region of two type-I quasi-stellar objects
We investigate the narrow-line region (NLR) of two radio-quiet QSOs,
PG1012+008 and PG1307+085, using high signal-to-noise spatially resolved
long-slit spectra obtained with FORS1 at the Very Large Telescope. Although the
emission is dominated by the point-spread function of the nuclear source, we
are able to detect extended NLR emission out to several kpc scales in both QSOs
by subtracting the scaled central spectrum from outer spectra. In contrast to
the nuclear spectrum, which shows a prominent blue wing and a broad line
profile of the [O III] line, the extended emission reveals no clear signs of
large scale outflows. Exploiting the wide wavelength range, we determine the
radial change of the gas properties in the NLR, i.e., gas temperature, density,
and ionization parameter, and compare them with those of Seyfert galaxies and
type-II QSOs. The QSOs have higher nuclear temperature and lower electron
density than Seyferts, but show no significant difference compared to type-II
QSOs, while the ionization parameter decreases with radial distance, similar to
the case of Seyfert galaxies. For PG1012+008, we determine the stellar velocity
dispersion of the host galaxy. Combined with the black hole mass, we find that
the luminous radio-quiet QSO follows the local M_BH-sigma* relation of active
galactic nuclei.Comment: 7 pages, 5 figures, accepted for publication in Ap
The AGN Population in X-ray Selected Galaxy Groups at
We use Chandra data to study the incidence and properties of Active Galactic
Nuclei (AGN) in 16 intermediate redshift () X-ray-selected
galaxy groups in the Chandra Deep Field-South. We measure an AGN fraction of
at ,
approximately a factor of two higher than the AGN fraction found for rich
clusters at comparable redshift. This extends the trend found at low redshift
for groups to have higher AGN fractions than clusters. Our estimate of the AGN
fraction is also more than a factor of 3 higher than that of low redshift
X-ray-selected groups. Using optical spectra from various surveys, we also
constrain the properties of emission-line selected AGN in these groups.
Contrary to the large population of X-ray AGN ( erg/s) =
25), we find only 4 emission-line AGN, 3 of which are also X-ray bright.
Furthermore, most of the X-ray AGN in our groups are optically-dull (i.e. lack
strong emission-lines) similar to those found in low redshift X-ray groups and
clusters of galaxies. This contrasts with the AGN population found in low
redshift optically-selected groups which are dominated by emission-line AGN.
The differences between the optically and X-ray-selected AGN populations in
groups are consistent with a scenario where most AGN in the densest
environments are currently in a low accretion state.Comment: 8 pages, 4 figures, accepted for publication in Ap
Spectroscopy of the Young Stellar Association Price-Whelan 1: Origin in the Magellanic Leading Arm and Constraints on the Milky Way Hot Halo
We report spectroscopic measurements of stars in the recently discovered
young stellar association Price-Whelan 1 (PW 1), which was found in the
vicinity of the Leading Arm (LA) of the Magellanic Stream. We obtained
Magellan+MIKE high-resolution spectra of the 28 brightest stars in PW 1 and
used The Cannon to determine their stellar parameters. We find that the mean
metallicity of PW 1 is [Fe/H]=-1.23 with a small scatter of 0.06 dex and the
mean radial velocity is Vhelio=276.7 km/s with a dispersion of 11.0 km/s. Our
results are consistent in Teff, logg, and [Fe/H] with the young and metal-poor
characteristics (116 Myr and [Fe/H]=-1.1) determined for PW 1 from our
discovery paper. We find a strong correlation between the spatial pattern of
the PW 1 stars and the LA II gas with an offset of -10.15 deg in L_MS and +1.55
deg in B_MS. The similarity in metallicity, velocity, and spatial patterns
indicates that PW 1 likely originated in LA II. We find that the spatial and
kinematic separation between LA II and PW 1 can be explained by ram pressure
from Milky Way gas. Using orbit integrations that account for the LMC and MW
halo and outer disk gas, we constrain the halo gas density at the orbital
pericenter of PW 1 to be n_halo (17 kpc) = 2.7 (3) x 10^-3 atoms/cm^3 and the
disk gas density at the midplane at 20 kpc to be n_disk (20 kpc,0) = 6.0 (1.8)
x 10^-2 atoms/cm^3. We, therefore, conclude that PW 1 formed from the LA II of
the Magellanic Stream, making it a powerful constraint on the Milky
Way-Magellanic interaction.Comment: 18 pages, 13 figures, 1 table, submitted to Ap
Comoving stars in the Gaia era
Comoving stars range from wide binaries to dense open clusters, and provide a unique window into the Milky Way. They are consequences of recent star formation which occurs highly clustered in giant molecular clouds, and the stellar and dynamical evolution that follows. Recent data releases from the Gaia astrometric mission together with the on-going large spectroscopic surveys provide an ideal playground to study the entire spectrum of comoving stars and illuminate the formation and disruption of these objects. This thesis contains a series of projects related to finding and characterizing comoving stars with the Gaia data. After a brief general introduction in Chapter 1, I develop a method to search for comoving pairs of stars using astrometric data based on a probabilistic model selection in Chapter 2. I apply the method to the first data release of the Gaia mission and find 13,085 pairs among 10,606 stars, which make up 4,555 comoving systems. I follow up two of these systems in detail. In Chapter 3, I study the metallicity and abundance differences of a wide binary, HD 240429 and HD 240430. I discuss the possible reasons for the significant and condensation temperature-dependent abundance differences between the two stars and argue that one of the stars has likely accreted a massive, rocky planetary system. In Chapter 4, I confirm and characterize the nearest and largest new comoving group discovered in Chapter 2, using the second data release of Gaia. I extend the candidate members and discuss its morphology in relation to its disruption