37 research outputs found
The CFHTLS Deep Catalog of Interacting Galaxies I. Merger Rate Evolution to z=1.2
We present the rest-frame optical galaxy merger fraction between 0.2<z<1.2,
as a function of stellar mass and optical luminosity, as observed by the
Canada-France-Hawaii Telescope Legacy Deep Survey (CFHTLS-Deep). We developed a
new classification scheme to identify major galaxy-galaxy mergers based on the
presence of tidal tails and bridges. These morphological features are signposts
of recent and ongoing merger activity. Through the visual classification of all
galaxies, down to i_vega<22.2 (~27,000 galaxies) over 2 square degrees, we have
compiled the CFHTLS Deep Catalog of Interacting Galaxies, with ~1600 merging
galaxies. We find the merger fraction to be 4.3% +/-0.3% at z~0.3 and 19.0%
+/-2.5% at z~1, implying evolution of the merger fraction going as (1+z)^m,
with m=2.25 +/-0.24. This result is inconsistent with a mild or non-evolving
(m4sigma level of confidence. A mild trend, where massive
galaxies with M>10^10.7 M_sun are undergoing fewer mergers than less massive
systems M~10^10 M_sun), consistent with the expectations of galaxy assembly
downsizing is observed. Our results also show that interacting galaxies have on
average SFRs double that found in non-interacting field galaxies. We conclude
that (1) the optical galaxy merger fraction does evolve with redshift, (2) the
merger fraction depends mildly on stellar mass, with lower mass galaxies having
higher merger fractions at z<1, and (3) star formation is triggered at all
phases of a merger, with larger enhancements at later stages, consistent with
N-body simulations.Comment: e.g.: 17 pages, 14 figures, accepted for publication in Ap
The Space Density Evolution of Wet and Dry Mergers in the Canada-France-Hawaii Telescope Legacy Survey
We analyze 1298 merging galaxies with redshifts up to z = 0.7 from the Canada-France-Hawaii Telescope Legacy Survey, taken from the catalog presented in Bridge et al. (2010). By analyzing the internal colors of these systems, we show that so-called wet and dry mergers evolve in different senses, and quantify the space densities of these systems. The local space density of wet mergers is essentially identical to the local space density of dry mergers. The evolution in the total merger rate is modest out to z ∼ 0.7, although the wet and dry populations have different evolutionary trends. At higher redshifts dry mergers make a smaller contribution to the total merging galaxy population, but this is offset by a roughly equivalent increase in the contribution from wet mergers. By comparing the mass density function of early-type galaxies to the corresponding mass density function for merging systems, we show that not all the major mergers with the highest masses (M_(stellar) > 10^(11)M☉) will end up with the most massive early-type galaxies, unless the merging timescale is dramatically longer than that usually assumed. On the other hand, the usually-assumed merging timescale of ∼ 0.5–1 Gyr is quite consistent with the data if we suppose that only less massive early-type galaxies form via mergers. Since low-intermediate mass ellipticals are 10–100 times more common than their most massive counterparts, the hierarchical explanation for the origin of early-type galaxies may be correct for the vast majority of early-types, even if incorrect for the most massive ones
The Space Density Evolution of Wet and Dry Mergers in the Canada-France-Hawaii Telescope Legacy Survey
We analyze 1298 merging galaxies with redshifts up to z=0.7 from the
Canada-France-Hawaii Telescope Legacy Survey, taken from the catalog presented
in Bridge et al. (2010). By analyzing the internal colors of these systems, we
show that so-called wet and dry mergers evolve in different senses, and
quantify the space densities of these systems. The local space density of wet
mergers is essentially dentical to the local space density of dry mergers. The
evolution in the total merger rate is modest out to z ~ 0.7, although the wet
and dry populations have different evolutionary trends. At higher redshifts dry
mergers make a smaller contribution to the total merging galaxy population, but
this is offset by a roughly equivalent increase in the contribution from wet
mergers. By comparing the mass density function of early-type galaxies to the
corresponding mass density function for merging systems, we show that not all
the major mergers with the highest masses (M_stellar > 10^11 M_solar) will end
up with the most massive early-type galaxies, unless the merging timescale is
dramatically longer than that usually assumed. On the other hand, the
usually-assumed merging timescale of ~ 0.5-1 Gyr is quite consistent with the
data if we suppose that only less massive early-type galaxies form via mergers.
Since low-intermediate mass ellipticals are 10 --100 times more common than
their most massive counterparts, the hierarchical explanation for the origin of
early-type galaxies may be correct for the vast majority of early-types, even
if incorrect for the most massive ones.Comment: 10 pages, 8 figures. Accepted by A
Interferometric Follow-Up of WISE Hyper-Luminous Hot, Dust-Obscured Galaxies
WISE has discovered an extraordinary population of hyper-luminous dusty
galaxies which are faint in the two bluer passbands (m and m) but are bright in the two redder passbands of WISE (m and
m). We report on initial follow-up observations of three of these
hot, dust-obscured galaxies, or Hot DOGs, using the CARMA and SMA
interferometer arrays at submm/mm wavelengths. We report continuum detections
at 1.3 mm of two sources (WISE J014946.17+235014.5 and WISE
J223810.20+265319.7, hereafter W0149+2350 and W2238+2653, respectively), and
upper limits to CO line emission at 3 mm in the observed frame for two sources
(W0149+2350 and WISE J181417.29+341224.8, hereafter W1814+3412). The 1.3 mm
continuum images have a resolution of 1-2 arcsec and are consistent with single
point sources. We estimate the masses of cold dust are 2.0 for W0149+2350 and 3.9 for W2238+2653,
comparable to cold dust masses of luminous quasars. We obtain 2 upper
limits to the molecular gas masses traced by CO, which are 3.3 and 2.3 for W0149+2350 and W1814+3412,
respectively. We also present high-resolution, near-IR imaging with WFC3 on the
Hubble Space Telescope for W0149+2653 and with NIRC2 on Keck for W2238+2653.
The near-IR images show morphological structure dominated by a single,
centrally condensed source with effective radius less than 4 kpc. No signs of
gravitational lensing are evident.Comment: 13 pages, 3 figures. ApJ in pres
A New Population of High-z, Dusty Lyα Emitters and Blobs Discovered by WISE: Feedback Caught in the Act?
By combining data from the NASA Wide-field Infrared Survey Explorer (WISE) mission with optical spectroscopy from the W. M. Keck telescope, we discover a mid-IR color criterion that yields a 78% success rate in identifying rare, typically radio-quiet, 1.6 ≾ z ≾ 4.6 dusty Lyα emitters (LAEs). Of these, at least 37% have emission extended on scales of 30-100 kpc and are considered Lyα "blobs" (LABs). The objects have a surface density of only ~0.1 deg^(–2), making them rare enough that they have been largely missed in deep, small area surveys. We measured spectroscopic redshifts for 92 of these galaxies, and find that the LAEs (LABs) have a median redshift of 2.3 (2.5). The WISE photometry coupled with data from Herschel (Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA) reveals that these galaxies are in the Hyper Luminous IR galaxy regime (L IR ≳ 10^(13)-10^(14) L_☉) and have warm colors. They are typically more luminous and warmer than other dusty, z ~ 2 populations such as submillimeter-selected galaxies and dust-obscured galaxies. These traits are commonly associated with the dust being illuminated by intense active galactic nucleus activity. We hypothesize that the combination of spatially extended Lyα, large amounts of warm IR-luminous dust, and rarity (implying a short-lived phase) can be explained if the galaxies are undergoing brief, intense "feedback" transforming them from an extreme dusty starburst/QSO into a mature galaxy
Spitzer Photometry of WISE-Selected Brown Dwarf and Hyper-Luminous Infrared Galaxy Candidates
We present Spitzer 3.6 and 4.5 m photometry and positions for a sample
of 1510 brown dwarf candidates identified by the WISE all-sky survey. Of these,
166 have been spectroscopically classified as objects with spectral types M(1),
L(7), T(146), and Y(12); Sixteen other objects are non-(sub)stellar in nature.
The remainder are most likely distant L and T dwarfs lacking spectroscopic
verification, other Y dwarf candidates still awaiting follow-up, and assorted
other objects whose Spitzer photometry reveals them to be background sources.
We present a catalog of Spitzer photometry for all astrophysical sources
identified in these fields and use this catalog to identify 7 fainter (4.5
m 17.0 mag) brown dwarf candidates, which are possibly wide-field
companions to the original WISE sources. To test this hypothesis, we use a
sample of 919 Spitzer observations around WISE-selected high-redshift
hyper-luminous infrared galaxy (HyLIRG) candidates. For this control sample we
find another 6 brown dwarf candidates, suggesting that the 7 companion
candidates are not physically associated. In fact, only one of these 7 Spitzer
brown dwarf candidates has a photometric distance estimate consistent with
being a companion to the WISE brown dwarf candidate. Other than this there is
no evidence for any widely separated ( 20 AU) ultra-cool binaries. As an
adjunct to this paper, we make available a source catalog of 7.33
objects detected in all of these Spitzer follow-up fields for use
by the astronomical community. The complete catalog includes the Spitzer 3.6
and 4.5 m photometry, along with positionally matched and
photometry from USNO-B; , , and photometry from 2MASS; and ,
, , and photometry from the WISE all-sky catalog