The occulting galaxy pair UGC 3995 : dust properties from HST and CALIFA data.

UGC 3995 is an interacting and occulting galaxy pair. UGC 3995B is a foreground face-on spiral and UGC 3995A a bright background spiral with an AGN. We present analysis of the dust in the disc of UGC 3995B based on archival Hubble Space Telescope (HST) WFPC2 and PPAK IFU data from the CALIFA survey’s first data release. From the HST F606W image, we construct an extinction map by modeling the isophotes of the background galaxy UGC 3995A and the resulting transmission through UGC 3995B. This extinction map of UGC 3995B shows several distinct spiral extinction features. The radial distribution of AV values declines slowly with peaks corresponding to the spiral structures. The distribution of AV values in the HST extinction map peaks near AV = 0.3–0.4. Beyond this point, the distribution of AV values drops like an exponential: N(AV) = N0 × e(−AV/0.5). The 0.5 value is higher than typical for a spiral galaxy. The outer arms may be tidally distended; the extinction in the corresponding interarm regions is small to an unusually small radius. To analyze the PPAK IFU data, we take the ratio of a fibre spectrum in the overlap region and the corresponding background fiber spectrum to construct an extinction curve. We fit the Cardelli, Clayton and Mathis (CCM) curve to the extinction curve of each fiber element in the overlap region. A map of the extinction constructed from PPEX IFU data-cubes shows the same spiral structure of the HST extinction map but the some differences in the distribution of the normalization of the CCM fits (AV). The inferred extinction slopes (RV) maps do not display any structure and a range of values partly due to the sampling effects of the disc by fibers, sometimes due to bad fits, and possibly partly due to some reprocessing of dust grains in the interacting disc. We compare these findings to our other analysis of an occulting pair with HST and IFU data. In both cases the canonical RV = 3.1 is not recovered even though there is enough signal in the extinction curve. We attribute this to mixing opaque and more transparent sections of the disc in each resolution element (~3′′ or 0.9 kpc). To illustrate the difficulty of imposing a RV = 3.1 law over a section of a spiral disc, we average all spectra and show how a fully gray extinction curve is recovered

The Loneliest Galaxies in the Universe: A GAMA and GalaxyZoo Study on Void Galaxy Morphology

The large-scale structure (LSS) of the universe is comprised of galaxy filaments, tendrils, and voids. The majority of the universe’s volume is taken up by these voids, which exist as underdense, but not empty, regions. The galaxies found inside voids are void galaxies and expected to be some of the most isolated objects in the universe. However, their standard morphology remains poorly studied. This study, using the Galaxy and Mass Assembly (GAMA) survey and Galaxy Zoo’s SDSS survey, aims to remedy this. To do so, survey results from GAMA have been plotted using the Sérsic index (n) to analyze morphology, while data from Galaxy Zoo’s crowdsourced study supplies a second analysis. For completeness purposes, we only include void galaxies identified by Alpaslan et al. 2014 with a redshift (z) between .08 and .215 and stellar mass (M*) between 109.35 and 1011.5. We then utilize Kolmogorov-Smirnov (KS) testing for significance. As a result, we conclude that, as supported by previous literature (Kreckel et al. 2014, Beygu et al. 2015, Beygu et al. 2016, Fraser-McKelvie et al. 2016, Pustilnik et al. 2019) , most void galaxies have a disky morphology with Sérsic index

Automating the Synthetic Field Method:Application to Sextans A

We have automated the ``Synthetic Field Method'' developed by Gonzalez et al.(1998) and used it to measure the opacity of the ISM in the Local Group dwarf galaxy Sextans A by using the changes in counts of background galaxies seen through the foreground system. The Sextans A results are consistent with the observational relation found by Cuillandre et al. (2001) between dust opacity and HI column density in the outer parts of M31.Comment: 4 pages, 6 figures, submitted for the proceedings of The Dynamics, Structure and History of Galaxies: A Workshop in Honour of Prof. Ken Freema

Spiral disk opacity from occulting galaxy pairs in the Sloan Digital Sky Survey.

A spiral galaxy partially overlapping a more distant elliptical offers a unique opportunity to measure the dust extinction in the foreground spiral. From the Sloan Digital Sky Survey (SDSS) DR4 spectroscopic sample, we selected 83 occulting galaxy pairs and measured disk opacity over the redshift range z ¼ 0:0Y0:2 with the goal of determining the recent evolution of disk dust opacity. The enrichment of the ISM changes over the lifetime of a disk, and it is reasonable to expect the dust extinction properties of spiral disks as a whole to change over their lifetime. When they do, the change will affect our measurements of galaxies over the observable universe. From the SDSS pairs we conclude that spiral disks show evidence of extinction to r2 effective radii. However, no evidence for recent evolution of disk opacity is evident, due to the limited redshift range and our inability to distinguish other factors on disk opacity such as the presence of spiral arms and Hubble type. Such effects also mask any relation between surface brightness and optical depth that has been found in nearby galaxies. Hence, we conclude that the SDSS spectral catalog is an excellent way to find occulting pairs and construct a uniform local sample. However, a higher resolution than that of the SDSS images is needed to disentangle the effects of spiral arms and Hubble type from evolution since z ¼ 0:2

The Sizes of Candidate z∼9−10z\sim9-10 Galaxies: confirmation of the bright CANDELS sample and relation with luminosity and mass

Recently, a small sample of six $z\sim9-10$ candidates was discovered in CANDELS that are $\sim10-20\times$ more luminous than any of the previous $z\sim9-10$ galaxies identified over the HUDF/XDF and CLASH fields. We measure the sizes of these candidates to map out the size evolution of galaxies from the earliest observable times. Their sizes are also used to provide a valuable constraint on whether these unusual galaxy candidates are at high redshift. Using galfit to derive sizes from the CANDELS F160W images of these candidates, we find a mean size of 0.13$\pm$0.02" (or 0.5$\pm$0.1 kpc at $z\sim9-10$). This handsomely matches the 0.6 kpc size expected extrapolating lower redshift measurements to $z\sim9-10$, while being much smaller than the 0.59" mean size for lower-redshift interlopers to $z\sim9-10$ photometric selections lacking the blue IRAC color criterion. This suggests that source size may be an effective constraint on contaminants from $z\sim9-10$ selections lacking IRAC data. Assuming on the basis of the strong photometric evidence that the Oesch et al. 2014 sample is entirely at $z\sim9-10$, we can use this sample to extend current constraints on the size-luminosity, size-mass relation, and size evolution of galaxies to $z\sim10$. We find that the $z\sim9-10$ candidate galaxies have broadly similar sizes and luminosities as $z\sim6$-8 counterparts with star-formation-rate surface densities in the range of $\rm \Sigma_{SFR}=1-20\, M_\odot~ yr^{-1}\, kpc^{-2}$. The stellar mass-size relation is uncertain, but shallower than those inferred for lower-redshift galaxies. In combination with previous size measurements at z=4-7, we find a size evolution of $(1+z)^{-m}$ with $m=1.0\pm0.1$ for $>0.3L^*_{z=3}$ galaxies, consistent with the evolution previously derived from $2 < z < 8$ galaxies.Comment: 9 figures, 5 tables, accepted by Ap

The onset of warps in Spitzer observations of edge-on spiral galaxies.

We analyse warps in the nearby edge-on spiral galaxies observed in the Spitzer/Infrared Array Camera (IRAC )4.5-μm band. In our sample of 24 galaxies, we find evidence of warp in 14 galaxies. We estimate the observed onset radii for the warps in a subsample of 10 galaxies. The dark matter distribution in each of these galaxies are calculated using the mass distribution derived from the observed light distribution and the observed rotation curves. The theoretical predictions of the onset radii for the warps are then derived by applying a self-consistent linear response theory to the obtained mass models for six galaxies with rotation curves in the literature. By comparing the observed onset radii to the theoretical ones, we find that discs with constant thickness can not explain the observations; moderately flaring discs are needed. The required flaring is consistent with the observations. Our analysis shows that the onset of warp is not symmetric in our sample of galaxies. We define a new quantity called the onsetasymmetry index and study its dependence on galaxy properties. The onset asymmetries in warps tend to be larger in galaxies with smaller disc scalelengths. We also define and quantify the global asymmetry in the stellar light distribution, that we call the edge-on asymmetry in edge-on galaxies. It is shown that in most cases the onset asymmetry in warp is actually anticorrelated with the measured edge-on asymmetry in our sample of edge-on galaxies and this could plausibly indicate that the surrounding dark matter distribution is asymmetric

The Ultraviolet Attenuation Law in Backlit Spiral Galaxies

(Abridged) The effective extinction law (attenuation behavior) in galaxies in the emitted ultraviolet is well known only for actively star-forming objects and combines effects of the grain properties, fine structure in the dust distribution, and relative distributions of stars and dust. We use GALEX, XMM Optical Monitor, and HST data to explore the UV attenuation in the outer parts of spiral disks which are backlit by other UV-bright galaxies, starting with candidates provided by Galaxy Zoo participants. Our analysis incorporates galaxy symmetry, using non-overlapping regions of each galaxy to derive error estimates on the attenuation measurements. The entire sample has an attenuation law close to the Calzetti et al. (1994) form; the UV slope for the overall sample is substantially shallower than found by Wild et al. (2011), a reasonable match to the more distant galaxies in our sample but not to the weighted combination including NGC 2207. The nearby, bright spiral NGC 2207 alone gives accuracy almost equal to the rest of our sample, and its outer arms have a very low level of foreground starlight. This "grey" law can be produced from the distribution of dust alone, without a necessary contribution from differential escape of stars from dense clouds. The extrapolation needed to compare attenution between backlit galaxies at moderate redshifts, and local systems from SDSS data, is mild enough to allow use of galaxy overlaps to trace the cosmic history of dust. For NGC 2207, the covering factor of clouds with small optical attenuation becomes a dominant factor farther into the ultraviolet, which opens the possibility that widespread diffuse dust dominates over dust in star-forming regions deep into the ultraviolet. Comparison with published radiative-transfer models indicates that the role of dust clumping dominates over differences in grain populations, at this spatial resolution.Comment: In press, Astronomical Journa

Evidence for the concurrent growth of thick discs and central mass concentrations from S4^4G imaging

We have produced $3.6\mu{\rm m}+4.5\mu{\rm m}$ vertically integrated radial luminosity profiles of 69 edge-on galaxies from the Spitzer Survey of Stellar Structure in Galaxies (S$^4$G). We decomposed the luminosity profiles into a disc and a central mass concentration (CMC). These fits, combined with thin/thick disc decompositions from our previous studies, allow us to estimate the masses of the CMCs, the thick discs, and the thin discs ($\mathcal{M}_{\rm CMC}$, $\mathcal{M}_{\rm T}$, and $\mathcal{M}_{\rm T}$). We obtained atomic disc masses ($\mathcal{M}_{\rm g}$) from the literature. We then consider the CMC and the thick disc to be dynamically hot components and the thin disc and the gas disc to be dynamically cold components. We find that the ratio between the mass of the hot components and that of the cold components, $(\mathcal{M}_{\rm CMC}+\mathcal{M}_{\rm T})/(\mathcal{M}_{\rm t}+\mathcal{M}_{\rm g})$, does not depend on the total galaxy mass as described by circular velocities ($v_{\rm c}$). We also find that the higher the $v_{\rm c}$, the more concentrated the hot component of a galaxy. We suggest that our results are compatible with having CMCs and thick discs built in a short and early high star forming intensity phase. These components were born thick because of the large scale height of the turbulent gas disc in which they originated. Our results indicate that the ratio between the star forming rate in the former phase and that of the formation of the thin disc is of the order of 10, but the value depends on the duration of the high star forming intensity phase.Comment: Accepted for publication in A&

Default parallels: The science potential of JWST parallel observations during TSO primary observations

The James Webb Space Telescope (JWST) will observe several stars for long cumulative durations while pursuing exoplanets as primary science targets for both Guaranteed Time Observations (GTO) and very likely General Observer (GO) programs. Here we argue in favor of an automatic default parallel program to observe, e.g., using the F200W/F277W filters or grism of NIRCAM/NIRISS in order to find high redshift (z (Formula Presented) 10) galaxies, cool red/brown dwarf substellar objects, solar system objects, and observations of serendipitous planetary transits. We argue here the need for automated exploratory astrophysical observations with unused JWST instruments during these long-duration exoplanet observations. Randomized fields that are observed in parallel mode reduce errors due to cosmic variance more effectively than single continuous fields of a typical wedding cake observing strategy. Hence, we argue that the proposed automated survey will explore a unique and rich discovery space in the high-redshift universe, Galactic structure, and solar system. We show that the GTO and highly probable GO target list of exoplanets covers the Galactic disk/halo and high redshift universe, mostly well out of the plane of the disk of the Milky Way. Exposure times are of the order of the CEERS GTO medium-deep survey in a single filter, comparable to CANDELS in Hubble Space Telescopeʼs surveys and deep fields. The area covered by NIRISS and NIRCam combined could accumulate to a half square degree surveyed