72 research outputs found
Sexually selected sentinels? Evidence of a role for intrasexual competition in sentinel behavior.
Although the evolutionary mechanisms that favor investment in cooperative behaviors have long been a focus of research, comparatively few studies have considered the role that sexual selection may play. For example, evolutionary explanations for sentinel behavior (where 1 individual assumes an elevated position and scans the surroundings while other group members forage nearby) have traditionally focused on the inclusive fitness benefits arising from its effects on predation risk, while its potential role in defense against intrasexual competitors remains largely unexplored. Here, we provide experimental evidence of a role for sentinel behavior in intrasexual competition, in a cooperatively breeding songbird, the white-browed sparrow weaver (Plocepasser mahali). First, dominant males sentinel substantially more than other group members (even when controlling for variation in age and body condition), consistent with a role for sentineling in intrasexual competition for mates and/or territory. Second, experimental playback of an unfamiliar male's solo song elicited a marked increase in sentineling by the dominant male, and the vocal response to the playback also positively predicted his sentinel effort following the simulated intrusion. A second experiment also suggests that sentineling may facilitate mounting rapid anti-intruder responses, as responses to intruder-playback occurred significantly earlier when the dominant male was sentineling rather than foraging at playback onset. Together, our findings provide rare support for the hypothesis that sentinel behavior plays a role in intrasexual competition, and so highlight the potential for sexually selected direct benefits to shape its expression in this and other social vertebrates
Dominance-related seasonal song production is unrelated to circulating testosterone in a subtropical songbird
AbstractCirculating testosterone (T) is widely considered to play a key role in the production of sexual displays by male vertebrates. While numerous studies support a role for circulating T in promoting the production of song in male birds, this understanding is based primarily on evidence from seasonally breeding northern temperate species, leaving it unclear whether this mechanism generalizes to other regions of the world. Here we investigate whether variation in circulating levels of T can explain the marked within- and among-individual variation in male song performance observed in a subtropical population of the year-round territorial white-browed sparrow weaver (Plocepasser mahali mahali). Our findings reveal that both circulating T and male song production peaked at a similar time point, halfway through the population-level breeding season. However, while dominant males were more likely to sing and sang for longer than subordinate males, within-group paired comparisons revealed no dominance-related differences in circulating T. Moreover, comparisons both among and within individual dominant males revealed that song duration, syllable rate and proportion of time spent singing were all unrelated to circulating T. Together, our findings suggest that natural variation in male song production, at least in this population of white-browed sparrow weavers, is achieved principally through mechanisms other than variation in circulating T concentration. More widely, our results are in line with the view that male song production is not exclusively regulated by gonadally synthesized steroids
Near Infrared Spectra and Intrinsic Luminosities of Candidate Type II Quasars at 2 < z < 3.4
We present JHK near-infrared (NIR) spectroscopy of 25 candidate Type II
quasars selected from the Sloan Digital Sky Survey, using Triplespec on the
Apache Point Observatory 3.5m telescope, FIRE at the Magellan/Baade 6.5m
telescope, and GNIRS on Gemini. At redshifts of 2 < z < 3.4, our NIR spectra
probe the rest-frame optical region of these targets, which were initially
selected to have strong lines of CIV and Ly alpha, with FWHM<2000 km/s from the
SDSS pipeline. We use the [OIII]5007 line shape as a model for the narrow line
region emission, and find that \halpha\ consistently requires a broad component
with FWHMs ranging from 1000 to 7500 km/s. Interestingly, the CIV lines also
require broad bases, but with considerably narrower widths of 1000 to 4500
km/s. Estimating the extinction using the Balmer decrement and also the
relationship in lower-z quasars between rest equivalent width and luminosity in
the [OIII] line, we find typical A_V values of 0-2 mag, which naturally explain
the attenuated CIV lines relative to Halpha. We propose that our targets are
moderately obscured quasars. We also describe one unusual object with three
distinct velocity peaks in its [OIII] spectrum.Comment: Accepted for publication in ApJ, 18 pages, 14 figure
Candidate Type II Quasars at 2 < z < 4.3 in the Sloan Digital Sky Survey III
At low redshifts, dust-obscured quasars often have strong yet narrow
permitted lines in the rest-frame optical and ultraviolet, excited by the
central active nucleus, earning the designation Type II quasars. We present a
sample of 145 candidate Type II quasars at redshifts between 2 and 4.3,
encompassing the epoch at which quasar activity peaked in the universe. These
objects, selected from the quasar sample of the Baryon Oscillation
Spectroscopic Survey of the Sloan Digital Sky Survey III, are characterized by
weak continuum in the rest-frame ultraviolet (typical continuum magnitude of i
\approx 22) and strong lines of CIV and Ly \alpha, with Full Width at Half
Maximum less than 2000 kms-1. The continuum magnitudes correspond to an
absolute magnitude of -23 or brighter at redshift 3, too bright to be due
exclusively to the host galaxies of these objects. Roughly one third of the
objects are detected in the shorter-wavelength bands of the WISE survey; the
spectral energy distributions (SEDs) of these objects appear to be intermediate
between classic Type I and Type II quasars seen at lower redshift. Five objects
are detected at rest frame 6\mu m by Spitzer, implying bolometric luminosities
of several times 10^46 erg s-1. We have obtained polarization measurements for
two objects; they are roughly 3% polarized. We suggest that these objects are
luminous quasars, with modest dust extinction (A_V ~ 0.5 mag), whose
ultraviolet continuum also includes a substantial scattering contribution.
Alternatively, the line of sight to the central engines of these objects may be
partially obscured by optically thick material.Comment: 26 pages, 13 figures, 10 tables, 4 machine readable tables. Accepted
for publication in MNRA
Type 2 Active Galactic Nuclei with Double-Peaked [OIII] Lines. II. Single AGNs with Complex Narrow-Line Region Kinematics are More Common than Binary AGNs
(Abridged) Approximately 1% of low redshift (z<0.3) optically-selected type 2
AGNs show a double-peaked [OIII] narrow emission line profile in their
spatially-integrated spectra. Such features are usually interpreted as due
either to kinematics, such as biconical outflows and/or disk rotation of the
narrow line region (NLR) around single black holes, or to the relative motion
of two distinct NLRs in a merging pair of AGNs. Here we report follow-up near
infrared (NIR) imaging and optical slit spectroscopy of 31 double-peaked [OIII]
type 2 AGNs drawn from the SDSS parent sample presented in Liu et al (2010).
These data reveal a mixture of origins for the double-peaked feature. Roughly
10% of our objects are best explained by binary AGNs at (projected) kpc-scale
separations, where two stellar components with spatially coincident NLRs are
seen. ~ 50% of our objects have [OIII] emission offset by a few kpc,
corresponding to the two velocity components seen in the SDSS spectra, but
there are no corresponding double stellar components seen in the NIR imaging.
For those objects with sufficiently high quality slit spectra, we see velocity
and/or velocity dispersion gradients in [OIII] emission, suggestive of the
kinematic signatures of a single NLR. The remaining ~40% of our objects are
ambiguous, and will need higher spatial resolution observations to distinguish
between the two scenarios. Our observations therefore favor the kinematics
scenario with a single AGN for the majority of these double-peaked [OIII] type
2 AGNs. We emphasize the importance of combining imaging and slit spectroscopy
in identifying kpc binary AGNs, i.e., in no cases does one of these alone allow
an unambiguous identification. We estimate that ~ 0.5-2.5% of the z<0.3 type 2
AGNs are kpc-scale binary AGNs of comparable luminosities, with a relative
orbital velocity >~150 km/s.Comment: Minor changes; ApJ in press; 71 pages with 40 figures; color print
preferred; a high-resolution version can be downloaded at
https://www.cfa.harvard.edu/~yshen/papers/double_o3_rv1.pd
The Stellar Halos of Massive Elliptical Galaxies
We use the Mitchell Spectrograph (formerly VIRUS-P) on the McDonald
Observatory 2.7m Harlan J. Smith Telescope to search for the chemical
signatures of massive elliptical galaxy assembly. The Mitchell Spectrograph is
an integral-field spectrograph with a uniquely wide field of view (107x107 sq
arcsec), allowing us to achieve remarkably high signal-to-noise ratios of
~20-70 per pixel in radial bins of 2-2.5 times the effective radii of the eight
galaxies in our sample. Focusing on a sample of massive elliptical galaxies
with stellar velocity dispersions sigma* > 150 km/s, we study the radial
dependence in the equivalent widths (EWs) of key metal absorption lines. By
twice the effective radius, the Mgb EWs have dropped by ~50%, and only a weak
correlation between sigma* and Mgb EW remains. The Mgb EWs at large radii are
comparable to those seen in the centers of elliptical galaxies that are
approximately an order of magnitude less massive. We find that the well-known
metallicity gradients often observed within an effective radius continue
smoothly to 2.5R_e, while the abundance ratio gradients remain flat. Much like
the halo of the Milky Way, the stellar halos of our galaxies have low
metallicities and high alpha-abundance ratios, as expected for very old stars
formed in small stellar systems. Our observations support a picture in which
the outer parts of massive elliptical galaxies are built by the accretion of
much smaller systems whose star formation history was truncated at early times.Comment: To appear in ApJ, 15 pages, 9 figure
Host Galaxies of Luminous Type 2 Quasars at z ~ 0.5
We present deep Gemini GMOS optical spectroscopy of nine luminous quasars at
redshifts z ~ 0.5, drawn from the SDSS type 2 quasar sample. Our targets were
selected to have high intrinsic luminosities (M_V < -26 mag) as indicated by
the [O III] 5007 A emission-line luminosity (L_[O III]). Our sample has a
median black hole mass of ~ 10^8.8 M_sun inferred assuming the local
M_BH-sigma_* relation and a median Eddington ratio of ~ 0.7, using stellar
velocity dispersions sigma_* measured from the G band. We estimate the
contamination of the stellar continuum from scattered quasar light based on the
strength of broad H-beta, and provide an empirical calibration of the
contamination as a function of L_[O III]; the scattered light fraction is ~ 30%
of L_5100 for objects with L_[O III] = 10^9.5 L_sun. Population synthesis
indicates that young post-starburst populations (< 0.1 Gyr) are prevalent in
luminous type 2 quasars, in addition to a relatively old population (> 1 Gyr)
which dominates the stellar mass. Broad emission complexes around He II 4686 A
with luminosities up to 10^8.3 L_sun are unambiguously detected in three out of
the nine targets, indicative of Wolf-Rayet populations. Population synthesis
shows that ~ 5-Myr post-starburst populations contribute substantially to the
luminosities (> 50% of L_5100) of all three objects with Wolf-Rayet detections.
We find two objects with double cores and four with close companions. Our
results may suggest that luminous type 2 quasars trace an early stage of galaxy
interaction, perhaps responsible for both the quasar and the starburst
activity.Comment: 20 pages, 13 figures, 7 tables; accepted to Ap
The Host Galaxies of Low-mass Black Holes
Using HST observations of 147 host galaxies of low-mass black holes (BHs), we
systematically study the structures and scaling relations of these active
galaxies. Our sample is selected to have central BHs with virial masses
~10^5-10^6 solar mass. The host galaxies have total I-band magnitudes of
-23.2<M_I<-18.8 mag and bulge magnitudes of -22.9<M_I<-16.1 mag. Detailed
bulge-disk-bar decompositions with GALFIT show that 93% of the galaxies have
extended disks, 39% have bars and 5% have no bulges at all at the limits of our
observations. Based on the Sersic index and bulge-to-total ratio, we conclude
that the majority of the galaxies with disks are likely to contain pseudobulges
and very few of these low-mass BHs live in classical bulges. The fundamental
plane of our sample is offset from classical bulges and ellipticals in a way
that is consistent with the scaling relations of pseudobulges. The sample has
smaller velocity dispersion at fixed luminosity in the Faber-Jackson plane,
compared with classical bulges and elliptical galaxies. The galaxies without
disks are structurally more similar to spheroidals than to classical bulges
according to their positions in the fundamental plane, especially the
Faber-Jackson projection. Overall, we suggest that BHs with mass < 10^6 solar
mass live in galaxies that have evolved secularly over the majority of their
history. A classical bulge is not a prerequisite to host a black hole.Comment: 49 pages, 9 figures, accepted by Ap
The X-ray properties of million solar mass black holes
We present new Chandra X-ray observations of seven low-mass black holes (~1e6
Msun) accreting at low Eddington ratios between -2.0<log L/Ledd<-1.5. We
compare the X-ray properties of these seven low-mass active galactic nuclei
(AGN) to a total of 73 other low-mass AGN in the literature with published
Chandra observations (with Eddington ratios extending from -2.0<log
L/Ledd<-0.1). We do not find any statistical differences between low- and
high-Eddington ratio low-mass AGN in the distributions of their X-ray to
ultraviolet luminosity ratios (aox), or in their X-ray spectral shapes.
Furthermore, the aox distribution of low-L/Ledd AGN displays an X-ray weak tail
that is also observed within high-L/Ledd objects. Our results indicate that
between -2<log L/Ledd<-0.1, there is no systematic change in the structure of
the accretion flow for active galaxies hosting 1e6 Msun black holes. We examine
the accuracy of current bolometric luminosity estimates for our low-L/Ledd
objects with new Chandra observations, and it is plausible that their Eddington
ratios could be underestimated by up to an order of magnitude. If so, then in
analogy with weak emission line quasars, we suggest that accretion from a
geometrically thick, radiatively inefficient `slim disk' could explain their
diverse properties in aox. Alternatively, if current Eddington ratios are in
fact correct (or overestimated), then the X-ray weak tail would imply that
there is diversity in disk/corona couplings among individual low-mass objects.
Finally, we conclude by noting that the aox distribution for low-mass black
holes may have favorable consequences for the epoch of cosmic reionization
being driven by AGN.Comment: 14 pages, 6 figures, 6 tables. Accepted for publication in Ap
Extremely red quasars from SDSS, BOSS and WISE: classification of optical spectra
Quasars with extremely red infrared-to-optical colours are an interesting
population that can test ideas about quasar evolution as well as orientation,
obscuration and geometric effects in the so-called AGN unified model. To
identify such a population we match the quasar catalogues of the Sloan Digital
Sky Survey (SDSS), the Baryon Oscillation Spectroscopic Survey (BOSS) to the
Wide-Field Infrared Survey Explorer (WISE) to identify quasars with extremely
high infrared-to-optical ratios. We identify 65 objects with r(AB)-W4(Vega)>14
mag (i.e., F_nu(22um)/F_nu(r) > ~1000). This sample spans a redshift range of
0.28<z<4.36 and has a bimodal distribution, with peaks at z~0.8 and z~2.5. It
includes three z>2.6 objects that are detected in the W4-band but not W1 or W2
(i.e., W1W2-dropouts). The SDSS/BOSS spectra show that the majority of the
objects are reddened Type 1 quasars, Type 2 quasars (both at low and high
redshift) or objects with deep low-ionization broad absorption lines (BALs)
that suppress the observed r-band flux. In addition, we identify a class of
Type 1 permitted broad-emission line objects at z~2-3 which are characterized
by emission line rest-frame equivalent widths (REWs) of >~150Ang , much larger
than those of typical quasars. In particular, 55% (45%) of the non-BAL Type 1s
with measurable CIV in our sample have REW(CIV) > 100 (150)Ang, compared to
only 5.8% (1.3%) for non-BAL quasars in BOSS. These objects often also have
unusual line ratios, such as very high NV/Ly-alpha ratios. These large REWs
might be caused by suppressed continuum emission analogous to Type 2 quasars;
however, there is no obvious mechanism in standard Unified Models to suppress
the continuum without also obscuring the broad emission lines.Comment: 21 pages, 3 tables, 19 figures. Published in MNRAS. Moderate changes
from the v
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