80 research outputs found
A photometrically and spectroscopically confirmed population of passive spiral galaxies
We have identified a population of passive spiral galaxies from photometry and integral field spectroscopy. We selected z < 0.035 spiral galaxies that have WISE colours consistent with little mid-infrared emission from warm dust. Matched aperture photometry of 51 spiral galaxies in ultraviolet, optical and mid-infrared show these galaxies have colours consistent with passive galaxies. Six galaxies form a spectroscopic pilot study and were observed using the Wide-Field Spectrograph to check for signs of nebular emission from star formation. We see no evidence of substantial nebular emission found in previous red spiral samples. These six galaxies possess absorption-line spectra with 4000 Å breaks consistent with an average luminosity-weighted age of 2.3 Gyr. Our photometric and integral field spectroscopic observations confirm the existence of a population of local passive spiral galaxies, implying that transformation into early-type morphologies is not required for the quenching of star formation
Heterogeneity of inverted calcium II H:K ratio cluster galaxies
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society The ratio of calcium II H plus H∊ to calcium II K inverts as a galaxy stellar population moves from being dominated by older stars to possessing more A and B class stars. This ratio – the H:K ratio – can serve as an indicator of stellar populations younger than 200 Myr. In this work, we provide a new method to determine H:K, and apply it to spectra taken of cluster galaxies in Abell 3888. Although H:K is on average systematically lower for the cluster than for a wider field sample, we show that H:K does not have a simple relationship with other indices such as the equivalent widths of Hδ and [O II] beyond having a high value for strong [O II] emission. Moreover, strongly inverted galaxies with H:K > 1.1 have no preferred location within the cluster and are only slightly lower in their velocity dispersions around the cluster compared to strongly emitting [O II] galaxies. Our results indicate that selecting galaxies on H:K inversion results in a heterogeneous sample formed via a mixture of pathways that likely includes, but may not be limited to, merging spiral galaxies, and quiescent galaxies accreting lower mass, gas-rich companions. In concert with other selection criteria, H:K can provide a means to select a more ‘pure’ passive sample or to aid in the selection of highly star-forming galaxies, especially where other spectral line indicators such as H α may not have been observed
Welcome to the Twilight Zone: The Mid-Infrared Properties of Poststarburst Galaxies
We investigate the optical and Wide-field Survey Explorer (WISE) colors of
"E+A" identified post-starburst galaxies, including a deep analysis on 190
post-starbursts detected in the 2{\mu}m All Sky Survey Extended Source Catalog.
The post-starburst galaxies appear in both the optical green valley and the
WISE Infrared Transition Zone (IRTZ). Furthermore, we find that post-starbursts
occupy a distinct region [3.4]-[4.6] vs. [4.6]-[12] WISE colors, enabling the
identification of this class of transitioning galaxies through the use of
broad-band photometric criteria alone. We have investigated possible causes for
the WISE colors of post-starbursts by constructing a composite spectral energy
distribution (SED), finding that mid-infrared (4-12{\mu}m) properties of
post-starbursts are consistent with either 11.3{\mu}m polycyclic aromatic
hydrocarbon emission, or Thermally Pulsating Asymptotic Giant Branch (TP-AGB)
and post-AGB stars. The composite SED of extended post- starburst galaxies with
22{\mu}m emission detected with signal to noise >3 requires a hot dust
component to produce their observed rising mid-infrared SED between 12 and
22{\mu}m. The composite SED of WISE 22{\mu}m non-detections (S/N<3), created by
stacking 22{\mu}m images, is also flat, requiring a hot dust component. The
most likely source of this mid-infrared emission of these E+A galaxies is a
buried active galactic nucleus. The inferred upper limit to the Eddington
ratios of post-starbursts are 1e-2 to 1e-4, with an average of 1e-3. This
suggests that AGNs are not radiatively dominant in these systems. This could
mean that including selections able to identify active galactic nuclei as part
of a search for transitioning and post-starburst galaxies would create a more
complete census of the transition pathways taken as a galaxy quenches its star
formation.Comment: 13 pages, 11 figures, accepted for publication in the Astrophysical
Journa
An Enigmatic 380 kpc Long Linear Collimated Galactic Tail
We present an intriguing, serendipitously-detected system consisting of an
S0/a galaxy, which we refer to as the "Kite", and a highly-collimated tail of
gas and stars that extends over 380 kpc and contains pockets of star formation.
In its length, narrowness, and linearity the Kite's tail is an extreme example
relative to known tails. The Kite (PGC 1000273) has a companion galaxy, Mrk
0926 (PGC 070409), which together comprise a binary galaxy system in which both
galaxies host active galactic nuclei. Despite this systems being previously
searched for signs of tidal interactions, the tail had not been discovered
prior to our identification as part of the validation process of the SMUDGes
survey for low surface brightness galaxies. We confirm the kinematic
association between various H knots along the tail, a small galaxy, and
the Kite galaxy using optical spectroscopy obtained with the Magellan telescope
and measure a velocity gradient along the tail. The Kite shares characteristics
common to those formed via ram pressure stripping ("jellyfish" galaxies) and
formed via tidal interactions. However, both scenarios face significant
challenges that we discuss, leaving open the question of how such an extreme
tail formed. We propose that the tail resulted from a three-body interaction
from which the lowest-mass galaxy was ejected at high velocity.Comment: Submitted to publication in MNRAS (comments welcome
The effect of minor and major mergers on the evolution of low excitation radio galaxies
We use deep, μ r lesssim 28 mag arcsec−2, r-band imaging from the Dark Energy Camera Legacy Survey to search for past, or ongoing, merger activity in a sample of 282 low-excitation radio galaxies (LERGs) at z 4σ excess of major mergers in the LERGs with M * lesssim 1011 M⊙, with 10 ± 1.5% of these active galactic nuclei involved in such large-scale interactions compared to 3.2 ± 0.4% of control galaxies. This excess of major mergers in LERGs decreases with increasing stellar mass, vanishing by M * > 1011.3 M⊙. These observations show that minor mergers do not fuel LERGs, and are consistent with typical LERGs being powered by accretion of matter from their halo. Where LERGs are associated with major mergers, these objects may evolve into more efficiently accreting active galactic nuclei as the merger progresses and more gas falls on to the central engine
A genome-wide scan for common alleles affecting risk for autism
Although autism spectrum disorders (ASDs) have a substantial genetic basis, most of the known genetic risk has been traced to rare variants, principally copy number variants (CNVs). To identify common risk variation, the Autism Genome Project (AGP) Consortium genotyped 1558 rigorously defined ASD families for 1 million single-nucleotide polymorphisms (SNPs) and analyzed these SNP genotypes for association with ASD. In one of four primary association analyses, the association signal for marker rs4141463, located within MACROD2, crossed the genome-wide association significance threshold of P < 5 × 10−8. When a smaller replication sample was analyzed, the risk allele at rs4141463 was again over-transmitted; yet, consistent with the winner's curse, its effect size in the replication sample was much smaller; and, for the combined samples, the association signal barely fell below the P < 5 × 10−8 threshold. Exploratory analyses of phenotypic subtypes yielded no significant associations after correction for multiple testing. They did, however, yield strong signals within several genes, KIAA0564, PLD5, POU6F2, ST8SIA2 and TAF1C
A new method to constrain the appearance and disappearance of observed jellyfish galaxy tails
Galaxie
Measurements of identified particle anisotropic flow in Cu plus Au and U plus U collisions by PHENIX experiment
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