128 research outputs found
The Presence of Weak Active Galactic Nuclei in High Redshift Star Forming Galaxies
We present [OIII 5007A] observations of the star forming galaxy HDF-BMZ1299
(z=1.598) using Keck Observatory's Adaptive Optics system with the
near-infrared integral field spectrograph OSIRIS. Using previous Halpha and
[NII] measurements of the same source, we are able for the first time to use
spatially resolved observations to place a high-redshift galaxy's substructure
on a traditional HII diagnostic diagram. We find that HDF-BMZ1299's spatially
concentrated nebular ratios in the central ~1.5 kiloparsec (0."2) are best
explained by the presence of an AGN: log([NII]/Halpha)=-0.22+/-0.05 and 2sigma
limit of log([OIII]/Hbeta)>0.26. The dominant energy source of this galaxy is
star formation, and integrating a single aperture across the galaxy yields
nebular ratios that are composite spectra from both AGN and HII regions. The
presence of an embedded AGN in HDF-BMZ1299 may suggest a potential
contamination in a fraction of other high-redshift star forming galaxies, and
we suggest that this may be a source of the "elevated" nebular ratios
previously seen in seeing-limited metallicity studies. HDF-BMZ1299's estimated
AGN luminosity is L_Halpha = 3.7e41 erg/s and L_[OIII] = 5.8e41 erg/s, making
it one of the lowest luminosity AGN discovered at this early epoch.Comment: 15 pages, 4 figures, ApJ Accepted, new version to be published
(updated text, figures, and table
Gas-phase metallicity gradients of TNG50 star-forming galaxies
We present the radial gas-phase, mass-weighted metallicity profiles and
gradients of the TNG50 star-forming galaxy population measured at redshifts
0--3. We investigate the redshift evolution of gradients and examine
relations between gradient steepness and galaxy properties. We find that TNG50
gradients are predominantly negative at all redshifts, although we observe
significant diversity among these negative gradients. We determine that the
gradient steepness of all galaxies increases approximately monotonically with
redshift at a roughly constant rate. This rate does not vary significantly with
galaxy mass. We observe a weak negative correlation between gradient steepness
and galaxy stellar mass at redshifts . However, when we normalize
gradients by a characteristic radius defined by the galactic star formation
distribution, we find that these normalized gradients remain invariant with
both stellar mass and redshift. We place our results in the context of previous
simulations and show that TNG50 high-redshift gradients are steeper than those
of models featuring burstier feedback, which may further highlight
high-redshift gradients as important discriminators of galaxy formation models.
We also find that redshift and TNG50 gradients are consistent
with the gradients observed in galaxies at these redshifts, although the
preference for flat gradients observed in redshift galaxies is not
present in TNG50. If future JWST and ELT observations validate these flat
gradients, it may indicate a need for simulation models to implement more
powerful radial gas mixing within the ISM, possibly via turbulence and/or
stronger windsComment: 24 pages, 14 figures, submitted to MNRA
Gas-phase metallicity gradients of TNG50 star-forming galaxies
We present the radial gas-phase, mass-weighted metallicity profiles and gradients of the TNG50 star-forming galaxy population measured at redshifts z = 0-3. We investigate the redshift evolution of gradients and examine relations between gradient (negative) steepness and galaxy properties. We find that TNG50 gradients are predominantly negative at all redshifts, although we observe significant diversity among these negative gradients. We determine that the gradients of all galaxies grow more negative with redshift at a roughly constant rate of approximately -0.02 dex kpc-1/Îz. This rate does not vary significantly with galaxy mass. We observe a weak negative correlation between gradient (negative) steepness and galaxy stellar mass at z < 2. However, when we normalize gradients by a characteristic radius defined by the galactic star formation distribution, we find that these normalized gradients do not vary significantly with either stellar mass or redshift. We place our results in the context of previous simulations and show that TNG50 high-redshift gradients are more negative than those of models featuring burstier feedback, which may further highlight high-redshift gradients as important discriminators of galaxy formation models. We also find that z = 0 and z = 0.5 TNG50 gradients are consistent with the gradients observed in galaxies at these redshifts, although the preference for flat gradients observed in redshift z â„ 1 galaxies is not present in TNG50. If future JWST (James Webb Space Telescope) and ELT (Extremely Large Telescope) observations validate these flat gradients, it may indicate a need for simulation models to implement more powerful radial gas mixing within the ISM (interstellar medium), possibly via turbulence and/or stronger winds
Identification of residues in the N-terminal PAS domains important for dimerization of Arnt and AhR
The basic helixâloopâhelix (bHLH).PAS dimeric transcription factors have crucial roles in development, stress response, oxygen homeostasis and neurogenesis. Their target gene specificity depends in part on partner protein choices, where dimerization with common partner Aryl hydrocarbon receptor nuclear translocator (Arnt) is an essential step towards forming active, DNA binding complexes. Using a new bacterial two-hybrid system that selects for loss of protein interactions, we have identified 22 amino acids in the N-terminal PAS domain of Arnt that are involved in heterodimerization with aryl hydrocarbon receptor (AhR). Of these, Arnt E163 and Arnt S190 were selective for the AhR/Arnt interaction, since mutations at these positions had little effect on Arnt dimerization with other bHLH.PAS partners, while substitution of Arnt D217 affected the interaction with both AhR and hypoxia inducible factor-1α but not with single minded 1 and 2 or neuronal PAS4. Arnt uses the same face of the N-terminal PAS domain for homo- and heterodimerization and mutational analysis of AhR demonstrated that the equivalent region is used by AhR when dimerizing with Arnt. These interfaces differ from the PAS ÎČ-scaffold surfaces used for dimerization between the C-terminal PAS domains of hypoxia inducible factor-2α and Arnt, commonly used for PAS domain interactions
The role of stellar mass and environment for cluster blue fraction, AGN fraction and star-formation indicators from a targeted analysis of Abell 1691
We present an analysis of the galaxy population of the intermediate X-ray
luminosity galaxy cluster, Abell 1691, from SDSS and Galaxy Zoo data to
elucidate the relationships between environment and galaxy stellar mass for a
variety of observationally important cluster populations that include the
Butcher-Oemler blue fraction, the active galactic nucleus (AGN) fraction and
other spectroscopic classifications of galaxies. From 342 cluster members, we
determine a cluster recession velocity of 21257+/-54 km/s and velocity
dispersion of 1009^+40_-36 km/s and show that although the cluster is fed by
multiple filaments of galaxies it does not possess significant sub-structure in
its core. We identify the AGN population of the cluster from a BPT diagram and
show that there is a mild increase in the AGN fraction with radius from the
cluster centre that appears mainly driven by high mass galaxies (log(stellar
mass)>10.8). Although the cluster blue fraction follows the same radial trend,
it is caused primarily by lower mass galaxies (log(stellar mass)<10.8).
Significantly, the galaxies that have undergone recent star-bursts or are
presently star-bursting but dust-shrouded (spectroscopic e(a) class galaxies)
are also nearly exclusively driven by low mass galaxies. We therefore suggest
that the Butcher-Oemler effect may be a mass-dependant effect. We also examine
red and passive spiral galaxies and show that the majority are massive
galaxies, much like the rest of the red and spectroscopically passive cluster
population. We further demonstrate that the velocity dispersion profiles of low
and high mass cluster galaxies are different. Taken together, we infer that the
duty cycle of high and low mass cluster galaxies are markedly different, with a
significant departure in star formation and specific star formation rates
observed beyond r_200 and we discuss these findings.Comment: 17 pages, 14 figures (one degraded due to size constraints), accepted
for publication in MNRA
Gas Accretion and Galactic Chemical Evolution: Theory and Observations
This chapter reviews how galactic inflows influence galaxy metallicity. The
goal is to discuss predictions from theoretical models, but particular emphasis
is placed on the insights that result from using models to interpret
observations. Even as the classical G-dwarf problem endures in the latest round
of observational confirmation, a rich and tantalizing new phenomenology of
relationships between , , SFR, and gas fraction is emerging both in
observations and in theoretical models. A consensus interpretation is emerging
in which star-forming galaxies do most of their growing in a quiescent way that
balances gas inflows and gas processing, and metal dilution with enrichment.
Models that explicitly invoke this idea via equilibrium conditions can be used
to infer inflow rates from observations, while models that do not assume
equilibrium growth tend to recover it self-consistently. Mergers are an overall
subdominant mechanism for delivering fresh gas to galaxies, but they trigger
radial flows of previously-accreted gas that flatten radial gas-phase
metallicity gradients and temporarily suppress central metallicities. Radial
gradients are generically expected to be steep at early times and then
flattened by mergers and enriched inflows of recycled gas at late times.
However, further theoretical work is required in order to understand how to
interpret observations. Likewise, more observational work is needed in order to
understand how metallicity gradients evolve to high redshifts.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics
and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by
Springer. 29 pages, 2 figure
Hybrids of the bHLH and bZIP Protein Motifs Display Different DNA-Binding Activities In Vivo vs. In Vitro
Minimalist hybrids comprising the DNA-binding domain of bHLH/PAS (basic-helix-loop-helix/Per-Arnt-Sim) protein Arnt fused to the leucine zipper (LZ) dimerization domain from bZIP (basic region-leucine zipper) protein C/EBP were designed to bind the E-box DNA site, CACGTG, targeted by bHLHZ (basic-helix-loop-helix-zipper) proteins Myc and Max, as well as the Arnt homodimer. The bHLHZ-like structure of ArntbHLH-C/EBP comprises the Arnt bHLH domain fused to the C/EBP LZ: i.e. swap of the 330 aa PAS domain for the 29 aa LZ. In the yeast one-hybrid assay (Y1H), transcriptional activation from the E-box was strong by ArntbHLH-C/EBP, and undetectable for the truncated ArntbHLH (PAS removed), as detected via readout from the HIS3 and lacZ reporters. In contrast, fluorescence anisotropy titrations showed affinities for the E-box with ArntbHLH-C/EBP and ArntbHLH comparable to other transcription factors (Kd 148.9 nM and 40.2 nM, respectively), but only under select conditions that maintained folded protein. Although in vivo yeast results and in vitro spectroscopic studies for ArntbHLH-C/EBP targeting the E-box correlate well, the same does not hold for ArntbHLH. As circular dichroism confirms that ArntbHLH-C/EBP is a much more strongly α-helical structure than ArntbHLH, we conclude that the nonfunctional ArntbHLH in the Y1H must be due to misfolding, leading to the false negative that this protein is incapable of targeting the E-box. Many experiments, including protein design and selections from large libraries, depend on protein domains remaining well-behaved in the nonnative experimental environment, especially small motifs like the bHLH (60â70 aa). Interestingly, a short helical LZ can serve as a folding- and/or solubility-enhancing tag, an important device given the focus of current research on exploration of vast networks of biomolecular interactions
The Double Galaxy Cluster Abell 2465 I. Basic Properties: Optical Imaging and Spectroscopy
Optical imaging and spectroscopic observations of the z = 0.245 double galaxy
cluster Abell 2465 are described. This object appears to be undergoing a major
merger. It is a double X-ray source and is detected in the radio at 1.4 GHz.
This paper investigates signatures of the interaction of the two components.
Redshifts were measured to determine velocity dispersions and virial radii of
each component. The technique of fuzzy clustering was used to assign membership
weights to the galaxies in each clump. Using redshifts of 93 cluster members
within 1.4 Mpc of the subcluster centres, the virial masses and anisotropy
parameters are derived. 37% of the spectroscopically observed galaxies show
emission lines and are predominantly star forming in the diagnostic diagram. No
strong AGN sources were found. The emission line galaxies tend to lie between
the two cluster centres with more near the SW clump. The luminosity functions
of the two subclusters differ. The NE component is similar to many rich
clusters, while the SW component has more faint galaxies. The NE clump's light
profile follows a single NFW profile with c = 10 while the SW is better fit
with an extended outer region and a compact inner core, consistent with
available X-ray data indicating that the SW clump has a cooling core. The
observed differences and properties of the two components of Abell 2465 are
interpreted to have been caused by a collision 2-4 Gyr ago, after which they
have moved apart and are now near their apocentres, although the start of a
merger remains a possibility. The number of emission line galaxies gives weight
to the idea that galaxy cluster collisions trigger star formation.Comment: 21 pages, 18 Figures Replaced typos, mostly in references To appear
in MNRAS, Accepted 2010 December 16. Received 2010 December 15; in original
form 2010 November 0
Gaia Data Release 2: Photometric content and validation
Aims. We describe the photometric content of the second data release of the Gaia project (Gaia DR2) and its validation along with the quality of the data. Methods. The validation was mainly carried out using an internal analysis of the photometry. External comparisons were also made, but were limited by the precision and systematics that may be present in the external catalogues used. Results. In addition to the photometric quality assessment, we present the best estimates of the three photometric passbands. Various colour-colour transformations are also derived to enable the users to convert between the Gaia and commonly used passbands. Conclusions. The internal analysis of the data shows that the photometric calibrations can reach a precision as low as 2 mmag on individual CCD measurements. Other tests show that systematic effects are present in the data at the 10 mmag level
Protocol for a statewide randomized controlled trial to compare three training models for implementing an evidence-based treatment
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