ABSTRACT We present the first results of the Gould's Belt Distances Survey (GOBELINS), a project aimed at measuring the proper motion and trigonometric parallax of a large sample of young stars in ...nearby regions using multi-epoch Very Long Baseline Array (VLBA) radio observations. Enough VLBA detections have now been obtained for 16 stellar systems in Ophiuchus to derive their parallax and proper motion. This leads to distance determinations for individual stars with an accuracy of 0.3 to a few percent. In addition, the orbits of six multiple systems were modelled by combining absolute positions with VLBA (and, in some cases, near-infrared) angular separations. Twelve stellar systems are located in the dark cloud Lynds 1688; the individual distances for this sample are highly consistent with one another and yield a mean parallax for Lynds 1688 of mas, corresponding to a distance pc. This represents an accuracy greater than 1%. Three systems for which astrometric elements could be measured are located in the eastern streamer (Lynds 1689) and yield an estimate of mas, corresponding to a distance pc. This suggests that the eastern streamer is located about 10 pc farther than the core, but this conclusion needs to be confirmed by observations of additional sources in the eastern streamer (currently being collected). From the measured proper motions, we estimate the one-dimensional velocity dispersion in Lynds 1688 to be 2.8 1.8 and 3.0 2.0 km s−1, in R.A. and decl., respectively; these are larger than, but still consistent within of, those found in other studies.
ABSTRACT
We have measured, at various wavelengths, the spiral arm pitch angles of a sample of distant spiral galaxies from the Hubble Space Telescope eXtreme Deep Field (XDF). According to density ...wave (DW) theory, we should detect colour jumps from red-to-blue across the spiral arms. Colour jumps are a consequence of large-scale shocks, which also generate the classic blue-to-red age/colour gradients, and have only been detected until now in nearby spiral galaxies. Our results indicate that colour jumps and gradients have been occurring in distant galaxies for at least the last 8 Gyr, in agreement with DW theory.
I present integrated colors and surface brightness fluctuation magnitudes in the mid-infrared (IR), derived from stellar population synthesis models that include the effects of the dusty envelopes ...around thermally pulsing asymptotic giant branch (TP-AGB) stars. The models are based on the Bruzual & Charlot CB* isochrones; they are single-burst, range in age from a few Myr to 14 Gyr, and comprise metallicities between Z = 0.0001 and Z = 0.04. I compare these models to mid-IR data of AGB stars and star clusters in the Magellanic Clouds, and study the effects of varying self-consistently the mass-loss rate, the stellar parameters, and the output spectra of the stars plus their dusty envelopes. I find that models with a higher than fiducial mass-loss rate are needed to fit the mid-IR colors of "extreme" single AGB stars in the Large Magellanic Cloud. Surface brightness fluctuation magnitudes are quite sensitive to metallicity for 4.5 m and longer wavelengths at all stellar population ages, and powerful diagnostics of mass-loss rate in the TP-AGB for intermediate-age populations, between 100 Myr and 2-3 Gyr.
In this article, we present the results of a series of 12 3.6 cm radio continuum observations of T Tau Sb, one of the companions of the famous young stellar object T Tauri. The data were collected ...roughly every 2 months between 2003 September and 2005 July with the Very Long Baseline Array (VLBA). Thanks to the remarkably accurate astrometry delivered by the VLBA, the absolute position of T Tau Sb could be measured with a precision typically better than about 100 mu as at each of the 12 observed epochs. The trajectory of T Tau Sb on the plane of the sky could therefore be traced very precisely and was modeled as the superposition of the trigonometric parallax of the source and an accelerated proper motion. The best fit yields a distance to T Tau Sb of 147.0 plus or minus 0.6 pc. The observed positions of T Tau Sb are in good agreement with recent infrared measurements, but they seem to favor a somewhat longer orbital period than that recently reported by Duchene and coworkers for the T Tau Sa/T Tau Sb system.
ABSTRACT
The observed properties of galaxies are strongly dependent on both their total stellar mass and their morphology. Furthermore, the environment is known to play a strong role in shaping them. ...The galaxy population in the local Universe that is located in virialized clusters is found to be red, poorly star-forming, and mostly composed of early morphological types. Towards a holistic understanding of the mechanisms that drive galaxy evolution, we exploit the spectrophotometric data from the WINGS and OmegaWINGS local galaxy cluster surveys, and study the role of both the local and the large-scale environments. We attempt to disentangle their effects from the intrinsic characteristics of the galaxies, in shaping the star formation activity at fixed morphological type and stellar mass. Using a sample of field galaxies from the same surveys for comparison, we analyse the effects of the environment, embodied by the local density, clustercentric distance, and close neighbours, respectively, on the star formation histories of cluster galaxies. We find that local effects have a more relevant impact on galaxy stellar properties than the large-scale environment, and that morphology needs to be taken into account to pinpoint the mechanisms that are driving the influence of clusters in galaxy evolution.
It is widely accepted that the distribution function of the masses of young star clusters is universal and can be purely interpreted as a probability density distribution function with a constant ...upper mass limit. As a result of this picture the masses of the most massive objects are exclusively determined by the size of the sample. Here we show, with very high confidence, that the masses of the most massive young star clusters in M33 decrease with increasing galactocentric radius in contradiction to the expectations from a model of a randomly sampled constant cluster mass function with a constant upper mass limit. Pure stochastic star formation is thereby ruled out. We use this example to elucidate how naive analysis of data can lead to unphysical conclusions.
Abstract
We continue to explore the relationship between the total number of globular clusters (GCs),
N
GC
, and the central black hole mass,
M
•
, in spiral galaxies. We present here results for the ...Sab galaxies NGC 3368, NGC 4736 (M94), and NGC 4826 (M64), and the Sm galaxy NGC 4395. The GC candidate selection is based on the (
u
* –
i
′
) versus (
i
′
–
K
s
) color–color diagram, and
i
′
-band shape parameters. We determine the
M
•
versus
N
GC
correlation for these spirals, plus NGC 4258, NGC 253, M104, M81, M31, and the Milky Way. We also redetermine the correlation for the elliptical sample in Harris et al., with updated galaxy types from Sahu et al. Additionally, we derive the total stellar galaxy mass,
M
*
, from its two-slope correlation with
N
GC
, and fit
M
•
versus
M
*
for both spirals and ellipticals. We obtain log
M
•
∝ (1.01 ± 0.13) log
N
GC
for ellipticals, and log
M
•
∝ (1.64 ± 0.24) log
N
GC
for late-type galaxies (LTGs). The linear
M
•
versus
N
GC
correlation in ellipticals could be due to statistical convergence through mergers, unlike the much steeper correlation for LTGs. However, in the
M
•
versus total stellar mass (
M
*
) parameter space, with
M
*
derived from its correlation with
N
GC
,
M
•
∝ (1.48 ± 0.18) log
M
*
for ellipticals, and
M
•
∝ (1.21 ± 0.16) log
M
*
for LTGs. The observed agreement between ellipticals and LTGs in this parameter space may imply that black holes and galaxies coevolve through
calm
accretion, active galactic nuclei feedback, and other secular processes.
We explore the relationship between globular cluster total number, NGC, and central black hole mass, M•, in spiral galaxies. Including cosmic scatter, log M• ∝ (1.64 ± 0.24) log NGC. Whereas in ...ellipticals the correlation is linear log M• ∝ (1.02 ± 0.10) log NGC, and hence could be due to statistical convergence through mergers, this mechanism cannot explain the much steeper correlation in spirals. Additionally, we derive total stellar galaxy mass, M*, from its two-slope correlation with NGC (Hudson et al. 2014). In the M• versus M* parameter space, with M* derived from NGC, M• ∝ (1.48 ± 0.18) log M* for ellipticals, and M• ∝ (1.21 ± 0.16) log M* for spirals. The observed agreement between ellipticals and spirals may imply that black holes and galaxies co-evolve through “calm” accretion, AGN feedback and other secular processes.
We present multiobject spectroscopic observations of 23 globular cluster candidates (GCCs) in the prototypical megamaser galaxy NGC 4258, carried out with the Optical System for Imaging and ...low-Intermediate-Resolution Integrated Spectroscopy instrument at the 10.4 m Gran Telescopio Canarias. The candidates have been selected based on the (u* − i′) versus (i′ − Ks) diagram, in the first application of the u*i′Ks method to a spiral galaxy. In the spectroscopy presented here, 70% of the candidates are confirmed as globular clusters (GCs). Our results validate the efficiency of the u*i′Ks method in the sparser GC systems of spirals, and given the downward correction to the total number of GCs, the agreement of the galaxy with the correlations between black hole mass and the total number and mass of GCs is actually improved. We find that the GCs, mostly metal-poor, corotate with the H i disk, even at large galactocentric distances.
Abstract
The study of the luminosity contribution from thermally pulsing asymptotic giant branch (TP-AGB) stars to the stellar populations of galaxies is crucial to determine their physical ...parameters (e.g., stellar mass and age). We use a sample of 84 nearby disk galaxies to explore diverse stellar population synthesis models with different luminosity contributions from TP-AGB stars. We fit the models to optical and near-infrared (NIR) photometry, on a pixel-by-pixel basis. The statistics of the fits show a preference for a low-luminosity contribution (i.e., high mass-to-light ratio in the NIR) from TP-AGB stars. Nevertheless, for 30%–40% of the pixels in our sample a high-luminosity contribution (hence low mass-to-light ratio in the NIR) from TP-AGB stars is favored. According to our findings, the mean TP-AGB star luminosity contribution in nearby disk galaxies may vary with Hubble type. This may be a consequence of the variation of the TP-AGB mass-loss rate with metallicity, if metal-poor stars begin losing mass earlier than metal-rich stars, because of a pre-dust wind that precedes the dust-driven wind.
PDF
