201 research outputs found
The Multiple Timescales of Optical Variability of the Blazar 3C 279 During the 2001-2002 Outburst
During 2001-2002 the optically violent variable (OVV) blazar 3C 279 un-
derwent the most intense outburst seen during the entire fourteen year history
that this quasar has been studied at Colgate University's Foggy Bottom Obser-
vatory (FBO). This study concentrates on ~1600 R-filter images taken during
this period of activity. This data set includes twenty-nine nights of
microvari- ability coverage. The outburst began in March 2001, after 3C 279 had
faded to its faintest level, R = 15.5, in four years. The source reached its
brightest level, R = 12.5, in the fourteen years of our study in August 2001,
at which time it became unobservable due to its proximity to the Sun. Upon
becoming observable again in mid-December 2001, 3C 279 fluctuated between R =
13.9 and R = 14.7, until a dramatic decrease in flux level in June-July 2002
brought the source back down to a level comparable to its pre-outburst state.
The source exhibited numerous week-long flares of approximately one magnitude
during the outburst period. Superposed on these flares were night-to-night
variations of up to one half magnitude and intra-night microvariability of up
to 0.13 magnitude in three hours. We use visual inspection of the light curve
as well as numerical timescale analysis tools (the autocorrelation function,
the structure function, and the power spectrum) to characterize the multiple
timescales of variability ranging from 1.5 years to several hours.Comment: 44 pages, 21 figures, 3 tables Accepted for publication in the
Astronomical Journa
The Dependence of Galaxy Properties on the Underlying 3D Matter Density Field at 2.0<z<2.5
We study the environmental effect of galaxy evolution as a function of the
underlying 3D dark matter density for the first time at , in which the
underlying matter density is reconstructed from galaxy and Ly forest
spectroscopy through dynamical forward modeling techniques. Utilizing these
maps, we investigate the dependence of the star formation activities and galaxy
types (mergers, submillimeter galaxies, active galactic nuclei, and quiescent
galaxies) on the matter overdensity and stellar mass. For the first
time, we are able to probe underdense regions () in addition to
overdensities. We find that star formation activity generally depend on the
stellar mass, not the matter density, except for high-mass galaxies
( M) which show a drop in star formation activities
by a factor of more than if they reside in high density regions with
. We also find: (1) an absence of mergers and submillimeter
galaxies in higher-density regions but otherwise no trend across lower-density
bins, (2) the increase of active galactic nuclei and quiescent galaxy
prevalence as a function of matter density, and (3) the increase of all
aforementioned categories with the stellar mass. These results indicate that
mass is the main driver of galaxy evolution. Nonetheless, we also find evidence
for environmental quenching, particularly for high-mass galaxies in
high-density environments. Our novel approach directly using reconstructed dark
matter density maps demonstrates the new capability of the environmental effect
studies in galaxy evolution at higher redshift.Comment: 21 pages, 11 figures, submitted to ApJ, comments welcom
A Multiwavelength Study of a Sample of 70 ΞΌm Selected Galaxies in the COSMOS Field. II. The Role of Mergers in Galaxy Evolution
We analyze the morphological properties of a large sample of 1503 70 ΞΌm selected galaxies in the COSMOS field spanning the redshift range 0.01 10^(12) L_β) being up to ~50%. We also find that the fraction of spirals drops dramatically with L_(IR). Minor mergers likely play a role in boosting the infrared luminosity for sources with low luminosities (L_(IR) 1 being difficult to classify and subject to the effects of bandpass shifting; therefore, these numbers can only be considered lower limits. At z 1, the fraction of major mergers is lower, but is at least 30%-40% for ULIRGs. In a comparison of our visual classifications with several automated classification techniques we find general agreement; however, the fraction of identified mergers is underestimated due to automated classification methods being sensitive to only certain timescales of a major merger. Although the general morphological trends agree with what has been observed for local (U)LIRGs, the fraction of major mergers is slightly lower than seen locally. This is in part due to the difficulty of identifying merger signatures at high redshift. The distribution of the U β V color of the galaxies in our sample peaks in the green valley (= 1.1) with a large spread at bluer and redder colors and with the major mergers peaking more strongly in the green valley than the rest of the morphological classes. We argue that, given the number of major gas-rich mergers observed and the relatively short timescale that they would be observable in the (U)LIRG phase, it is plausible for the observed red sequence of massive ellipticals (<10^(12) M_β) to have been formed entirely by gas-rich major mergers
A Far-infrared Characterization of 24 ΞΌm Selected Galaxies at 0 < z < 2.5 using Stacking at 70 ΞΌm and 160 ΞΌm in the COSMOS Field
We present a study of the average properties of luminous infrared galaxies detected directly at 24 ΞΌm in the COSMOS field using a median stacking analysis at 70 ΞΌm and 160 ΞΌm. Over 35,000 sources spanning 0 β€ z β€ 3 and 0.06 mJy β€ S_(24) β€ 3.0 mJy are stacked, divided into bins of both photometric redshift and 24 ΞΌm flux. We find no correlation of S_(70)/S_(24) flux density ratio with S_(24), but find that galaxies with higher S_(24) have a lower S_(160)/S_(24) flux density ratio. These observed ratios suggest that 24 ΞΌm selected galaxies have warmer spectral energy distributions (SEDs) at higher mid-IR fluxes, and therefore have a possible higher fraction of active galactic nuclei. Comparisons of the average S_(70)/S_(24) and S_(160)/S_(24) colors with various empirical templates and theoretical models show that the galaxies detected at 24 ΞΌm are consistent with "normal" star-forming galaxies and warm mid-IR galaxies such as Mrk 231, but inconsistent with heavily obscured galaxies such as Arp 220. We perform a Ο^2 analysis to determine best-fit galactic model SEDs and total IR luminosities for each of our bins. We compare our results to previous methods of estimating L IR and find that previous methods show considerable agreement over the full redshift range, except for the brightest S_(24) sources, where they overpredict the bolometric IR luminosity at high redshift, most likely due to their warmer dust SED. We present a table that can be used as a more accurate and robust method for estimating bolometric infrared luminosity from 24 ΞΌm flux densities
A controlled study of cold dust content in galaxies from
At , the formation of new stars is dominated by dusty galaxies whose
far-IR emission indicates they contain colder dust than local galaxies of a
similar luminosity. We explore the reasons for the evolving IR emission of
similar galaxies over cosmic time using: 1) Local galaxies from GOALS ; 2) Galaxies at from the 5MUSES
(); 3) IR luminous galaxies spanning
from GOODS and Spitzer xFLS (). All
samples have Spitzer mid-IR spectra, and Herschel and ground-based
submillimeter imaging covering the full IR spectral energy distribution,
allowing us to robustly measure ,
, and for every galaxy. Despite similar infrared
luminosities, dusty star forming galaxies have a factor of 5 higher
dust masses and 5K colder temperatures. The increase in dust mass is linked
with an increase in the gas fractions with redshift, and we do not observe a
similar increase in stellar mass or star formation efficiency.
, a proxy
for , is strongly correlated with independently of redshift. We
measure merger classification and galaxy size for a subsample, and there is no
obvious correlation between these parameters and or . In dusty star forming galaxies, the
change in can fully
account for the observed colder dust temperatures, suggesting that any change
in the spatial extent of the interstellar medium is a second order effect.Comment: Accepted for publication in ApJ. 21 pages, 11 figure
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