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

Una Alemana en Panamá

Vivo en el norte de Alemania, cerca de Hanóver, pero como Stuttgart es la única universidad en Alemania (sin contar la universidad militar en Munich) donde se puede estudiar mi carrera, desde el inicio y no como especialización de ingeniería mecánica, escogí estudiar en el sudoeste de mi país. Los primeros dos años tuvimos cálculo, física, mecánica y electrotecnia junto con los estudiantes de mecánica. Además estudiamos termodinámica, materiales, diseño de vehículos aéreos y análisis numérico

The Luminosity Function at z~8 from 97 Y-band dropouts: Inferences About Reionization

[Abbreviated] We present the largest search to date for $z\sim8$ Lyman break galaxies (LBGs) based on 350 arcmin$^2$ of HST observations in the V-, Y-, J- and H-bands from the Brightest of Reionizing Galaxies (BoRG) survey. The BoRG dataset includes $\sim$50 arcmin$^2$ of new data and deeper observations of two previous BoRG pointings, from which we present 9 new $z\sim8$ LBG candidates, bringing the total number of BoRG LBGs to 38 with $25.5\leqslant m_{J} \leqslant 27.6$ (AB system). We introduce a new Bayesian formalism for estimating the galaxy luminosity function (LF), which does not require binning (and thus smearing) of the data and includes a likelihood based on the formally correct binomial distribution as opposed to the often used approximate Poisson distribution. We demonstrate the utility of the new method on a sample of $97$ LBGs that combines the bright BoRG galaxies with the fainter sources published in Bouwens et al. (2012) from the HUDF and ERS programs. We show that the $z\sim8$ LF is well described by a Schechter function with a characteristic magnitude $M^\star = -20.15^{+0.29}_{-0.38}$, a faint-end slope of $\alpha = -1.87^{+0.26}_{-0.26}$, and a number density of $\log_{10} \phi^\star [\textrm{Mpc}^{-3}] = -3.24^{+0.25}_{-0.24}$. Integrated down to $M=-17.7$ this LF yields a luminosity density, $\log_{10} \epsilon [\textrm{erg}/\textrm{s/Hz/Mpc}^{3}] = 25.52^{+0.05}_{-0.05}$. Our LF analysis is consistent with previously published determinations within 1$\sigma$. We discuss the implication of our study for the physics of reionization. By assuming theoretically motivated priors on the clumping factor and the photon escape fraction we show that the UV LF from galaxy samples down to $M=-17.7$ can ionize only 10-50% of the neutral hydrogen at $z\sim8$. Full reionization would require extending the LF down to $M=-15$.Comment: Accepted for publication in ApJ, 22 pages, 15 figure

The dependence of the AV prior for SN Ia on host mass and disc inclination.

Type Ia supernovae (SNe Ia) are used as ‘standard candles’ for cosmological distance scales. To fit their light-curve shape–absolute luminosity relation, one needs to assume an intrinsic colour and a likelihood of host galaxy extinction or a convolution of these, a colour distribution prior. The host galaxy extinction prior is typically assumed to be an exponential drop-off for the current supernova programmes ( P(AV)∝e−AV/τ0 role= presentation style= box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline-table; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative; \u3eP(AV)∝e−AV/τ0P(AV)∝e−AV/τ0 ). We explore the validity of this prior using the distribution of extinction values inferred when two galaxies accidentally overlap (an occulting galaxy pair). We correct the supernova luminosity distances from the SDSS-III supernova projects (SDSS-SN) by matching the host galaxies to one of three templates from occulting galaxy pairs based on the host galaxy mass and the AV-bias–prior-scale (τ0) relation from Jha et al. We find that introducing an AV prior that depends on host mass results in lowered luminosity distances for the SDSS-SN on average but it does not reduce the scatter in individual measurements. This points, in our view, to the need for many more occulting galaxy templates to match to SN Ia host galaxies to rule out this possible source of scatter in the SN Ia distance measurements. We match occulting galaxy templates based on both mass and projected radius and we find that one should match by stellar mass first with radius as a secondary consideration. We discuss the caveats of the current approach: the lack of enough radial coverage, the small sample of priors (occulting pairs with HST data), the effect of gravitationally interacting as well as occulting pairs, and whether an exponential distribution is appropriate. Our aim is to convince the reader that a library of occulting galaxy pairs observed with HST will provide sufficient priors to improve (optical) SN Ia measurements to the next required accuracy in cosmology

The observable supernova rate in galaxy–galaxy lensing systems with the TESS satellite

The Transiting Exoplanet Survey Satellite (TESS) is the latest observational effort to find exoplanets and map bright transient optical phenomena. Supernovae (SNe) are particularly interesting as cosmological standard candles for cosmological distance measures. The limiting magnitude of TESS strongly constrains SN detection to the very nearby Universe (m ∼ 19, z \u3c 0.05). We explore the possibility that more distant SNe that are gravitationally lensed and magnified by a foreground galaxy can be detected by TESS, an opportunity to measure the time delay between light paths and constrain the Hubble constant independently. We estimate the rate of occurrence of such systems, assuming reasonable distributions of magnification, host dust attenuation, and redshift. There are approximately 16 Type Ia SNe (SNIa) and 43 core-collapse SNe (SNcc) expected to be observable with TESS each year, which translates to 18 and 43 per cent chance of detection per year, respectively. Monitoring the largest collections of known strong galaxy–galaxy lenses from Petrillo et al., this translates into 0.6 and 1.3 per cent chances of an SNIa and an SNcc per year. The TESS all-sky detection rates are lower than those of the Zwicky Transient Facility and Vera Rubin Observatory. However, on the ecliptic poles, TESS performs almost as well as its all-sky search, thanks to its continuous coverage: 2 and 4 per cent chance of an observed SN (Ia or cc) each year. These rates argue for timely processing of full-frame TESS imaging to facilitate follow-up and should motivate further searches for low-redshift lensing system

An extended dust disk in a spiral galaxy : an occulting galaxy pair in the ACS nearby galaxy survey treasury.

We present an analysis of an occulting galaxy pair, serendipitously discovered in the ACS Nearby Galaxy Survey Treasury observations of NGC 253 taken with the Hubble Space Telescope’s (HST) Advanced Camera for Surveys in F475W, F606W, and F814W (SDSS − g, broad V, and I). The foreground disk system (at z 0.06) shows a dusty disk much more extended than the starlight, with spiral lanes seen in extinction out to 1.5 R25, approximately 6 half-light radii. This pair is the first where extinction can be mapped reliably out to this distance from the center. The spiral arms of the extended dust disk show typical extinction values of AF475W ∼ 0.25, AF606W ∼ 0.25, and AF814W ∼ 0.15. The extinction law inferred from these measures is similar to that of the local Milky Way, and we show that the smoothing effects of sampling at limited spatial resolution (\u3c 57 pc, in these data) flattens the observed function through mixing of regions with different extinction. This galaxy illustrates the diversity of dust distributions in spirals, and the limitations of adopting a single dust model for optically similar galaxies. The ideal geometry of this pair of overlapping galaxies and the high sampling of HST data make this data set ideal to analyze this pair with three separate approaches to overlapping galaxies: (1) a combined fit, rotating copies of both galaxies, (2) a simple flip of the background image, and (3) an estimate of the original fluxes for the individual galaxies based on reconstructions of their proper isophotes. We conclude that in the case of high-quality data such as these, isophotal models are to be preferred

Galaxy And Mass Assembly: Galaxy Zoo spiral arms and star formation rates

Understanding the effect spiral structure has on star formation properties of galaxies is important to complete our picture of spiral structure evolution. Previous studies have investigated connections between spiral arm properties and star formation, but the effect that the number of spiral arms has on this process is unclear. Here, we use the Galaxy And Mass Assembly (GAMA) survey paired with the citizen science visual classifications from the Galaxy Zoo project to explore galaxies’ spiral arm number and how it connects to the star formation process. We use the votes from the GAMA-Kilo Degree Survey Galaxy Zoo classification to investigate the link between spiral arm number and stellar mass, star formation rate, and specific star formation rate (sSFR). We find that galaxies with fewer spiral arms have lower stellar masses and higher sSFRs, while those with more spiral arms tend towards higher stellar masses and lower sSFRs, and conclude that galaxies are less efficient at forming stars if they have more spiral arms. We note how previous studies’ findings may indicate a cause for this connection in spiral arm strength or opacity