1,194 research outputs found
New Mural Graces Linfield French Classroom Wall
Thanks to five Linfield College student artists, the Linfield French room in 302 Walker Hall is now home to a mural. The mural is an inspired representation of today’s Francophone world
The Cepheid distance to the maser-host galaxy NGC 4258: Studying systematics with the Large Binocular Telescope
We identify and phase a sample of 81 Cepheids in the maser-host galaxy NGC
4258 using the Large Binocular Telescope (LBT), and obtain calibrated mean
magnitudes in up to 4 filters for a subset of 43 Cepheids using archival HST
data. We employ 3 models to study the systematic effects of extinction, the
assumed extinction law, and metallicity on the Cepheid distance to NGC 4258. We
find a correction to the Cepheid colors consistent with a grayer extinction law
in NGC 4258 compared to the Milky Way (), although we believe this is
indicative of other systematic effects. If we combine our Cepheid sample with
previously known Cepheids, we find a significant metallicity adjustment to the
distance modulus of mag/dex, for the Zaritsky et
al. (1994) metallicity scale, as well as a weak trend of Cepheid colors with
metallicity. Conclusions about the absolute effect of metallicity on Cepheid
mean magnitudes appear to be limited by the available data on the metallicity
gradient in NGC 4258, but our Cepheid data require at least some metallicity
adjustment to make the Cepheid distance consistent with independent distances
to the LMC and NGC 4258. From our ensemble of models and the geometric maser
distance of NGC 4258 ( mag), we estimate
mag ( kpc).Comment: Accepted for publication in MNRAS. 28 pages, 13 figures, 11 tables. A
brief video summarizing the key results of this paper can be found at
http://youtu.be/ICTTNyxZ89
The Efficacy of Galaxy Shape Parameters in Photometric Redshift Estimation: A Neural Network Approach
We present a determination of the effects of including galaxy morphological parameters in photometric redshift estimation with an artificial neural network method. Neural networks, which recognize patterns in the information content of data in an unbiased way, can be a useful estimator of the additional information contained in extra parameters, such as those describing morphology, if the input data are treated on an equal footing. We use imaging and five band photometric magnitudes from the All-wavelength Extended Groth Strip International Survey. It is shown that certain principal components of the morphology information are correlated with galaxy type. However, we find that for the data used the inclusion of morphological information does not have a statistically significant benefit for photometric redshift estimation with the techniques employed here. The inclusion of these parameters may result in a trade-off between extra information and additional noise, with the additional noise becoming more dominant as more parameters are added
Polars Changing State: Multiwavelength Long Term Photometry and Spectroscopy of QS Tel, V834 Cen, and BL Hyi
Long term optical and near-infrared photometric and blue spectroscopic
observations were obtained for QS Tel, V834 Cen, and BL Hyi. The optical light
curves of all three polars displayed large magnitude changes during our
observations. These same high/low state transitions were also apparent in
near-infrared JHK photometry, though with decreased amplitude. The color of the
polar with respect to its state was examined and found not to be a good
indicator of the instantaneous state. During low to high state transitions, a
nearly constant magnitude difference was observed in all three polars. This
m value was found to be consistent with the level expected to occur if
accretion onto the white dwarf reached the Eddington luminosity during the high
state. The high state Balmer decrement was measured for each star and used to
estimate that the temperature of the emission line forming region was ~12,000K
with N near 12.8 dex. No relationship between the Balmer emission line
strength and the white dwarf magnetic field strength was seen, in contrast to a
good correlation between these two parameters observed for UV emission lines.Comment: 9 figures, 4 tables; accepted for publication in PAS
Groups of Galaxies in AEGIS: The 200 ksec Chandra Extended X-ray Source catalogue
We present the discovery of seven X-ray emitting groups of galaxies selected
as extended X-ray sources in the 200 ksec Chandra coverage of the
All-wavelength Extended Groth Strip International Survey (AEGIS). In addition,
we report on AGN activity associated to these systems. Using the DEEP2 Galaxy
Redshift Survey coverage, we identify optical counterparts and determine
velocity dispersions. In particular, we find three massive high-redshift groups
at z>0.7, one of which is at z=1.13, the first X-ray detections of
spectroscopically selected DEEP2 groups. We also present a first look at the
the L_X-T, L_X-sigma, and sigma-T scaling relations for high-redshift massive
groups. We find that the properties of these X-ray selected systems agree well
with the scaling relations of similar systems at low redshift, although there
are X-ray undetected groups in the DEEP2 catalogue with similar velocity
dispersions. The other three X-ray groups with identified redshifts are
associated with lower mass groups at z~0.07 and together form part of a large
structure or "supergroup" in the southern portion of the AEGIS field. All of
the low-redshift systems are centred on massive elliptical galaxies, and all of
the high-redshift groups have likely central galaxies or galaxy pairs. All of
the central group galaxies host X-ray point sources, radio sources, and/or show
optical AGN emission. Particularly interesting examples of central AGN activity
include a bent-double radio source plus X-ray point source at the center of a
group at z=0.74, extended radio and double X-ray point sources associated to
the central galaxy in the lowest-redshift group at z=0.066, and a bright green
valley galaxy (part of a pair) in the z=1.13 group which shows optical AGN
emission lines.Comment: accepted to MNRAS, 15 pages, 11 figures, for version with full
resolution figures see http://www.ucolick.org/~tesla/aegis_groups.ps.g
Absence of Evidence Is Not Evidence of Absence: The Color-Density Relation at Fixed Stellar Mass Persists to z ~ 1
We use data drawn from the DEEP2 Galaxy Redshift Survey to investigate the
relationship between local galaxy density, stellar mass, and rest-frame galaxy
color. At z ~ 0.9, we find that the shape of the stellar mass function at the
high-mass (log (M*/Msun) > 10.1) end depends on the local environment, with
high-density regions favoring more massive systems. Accounting for this stellar
mass-environment relation (i.e., working at fixed stellar mass), we find a
significant color-density relation for galaxies with 10.6 < log(M*/Msun) < 11.1
and 0.75 < z < 0.95. This result is shown to be robust to variations in the
sample selection and to extend to even lower masses (down to log(M*/Msun) ~
10.4). We conclude by discussing our results in comparison to recent works in
the literature, which report no significant correlation between galaxy
properties and environment at fixed stellar mass for the same redshift and
stellar mass domain. The non-detection of environmental dependence found in
other data sets is largely attributable to their smaller samples size and lower
sampling density, as well as systematic effects such as inaccurate redshifts
and biased analysis techniques. Ultimately, our results based on DEEP2 data
illustrate that the evolutionary state of a galaxy at z ~ 1 is not exclusively
determined by the stellar mass of the galaxy. Instead, we show that local
environment appears to play a distinct role in the transformation of galaxy
properties at z > 1.Comment: 10 pages, 5 Figures; Accepted for publication in MNRA
Identifying parents with risky alcohol consumption habits in apaediatric unit – are screening and brief interventionappropriate methods?
X-ray selected AGN in groups at redshifts z~1
We explore the role of the group environment in the evolution of AGN at the
redshift interval 0.7<z<1.4, by combining deep Chandra observations with
extensive optical spectroscopy from the All-wavelength Extended Groth strip
International Survey (AEGIS). The sample consists of 3902 optical sources and
71 X-ray AGN. Compared to the overall optically selected galaxy population,
X-ray AGN are more frequently found in groups at the 99% confidence level. This
is partly because AGN are hosted by red luminous galaxies, which are known to
reside, on average, in dense environments. Relative to these sources, the
excess of X-ray AGN in groups is significant at the 91% level only. Restricting
the sample to 0.7<z<0.9 and M_B<-20mag in order to control systematics we find
that X-ray AGN represent (4.7\pm1.6) and (4.5\pm1.0)% of the optical galaxy
population in groups and in the field respectively. These numbers are
consistent with the AGN fraction in low redshift clusters, groups and the
field. The results above, although affected by small number statistics, suggest
that X-ray AGN are spread over a range of environments, from groups to the
field, once the properties of their hosts (e.g. colour, luminosity) are
accounted for. There is also tentative evidence, significant at the 98% level,
that the field produces more X-ray luminous AGN compared to groups, extending
similar results at low redshift to z~1. This trend may be because of either
cold gas availability or the nature of the interactions occurring in the denser
group environment (i.e. prolonged tidal encounters).Comment: To appear in MNRA
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