اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدGalaxy Zoo: A Catalog of Overlapping Galaxy Pairs for Dust Studies
111
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Analysis of galaxies with overlapping images offers a direct way to probe the distribution of dust extinction and its effects on the background light. We present a catalog of 1990 such galaxy pairs selected from the Sloan Digital Sky Survey (SDSS) by volunteers of the Galaxy Zoo project. We highlight subsamples which are particularly useful for retrieving such properties of the dust distribution as UV extinction, the extent perpendicular to the disk plane, and extinction in the inner parts of disks. The sample spans wide ranges of morphology and surface brightness, opening up the possibility of using this technique to address systematic changes in dust extinction or distribution with galaxy type. This sample will form the basis for forthcoming work on the ranges of dust distributions in local disk galaxies, both for their astrophysical implications and as the low-redshift part of a study of the evolution of dust properties. Separate lists and figures show deep overlaps, where the inner regions of the foreground galaxy are backlit, and the relatively small number of previously-known overlapping pairs outside the SDSS DR7 sky coverage.
قيم البحث
اقرأ أيضاً
We investigate the effect of dust on spiral galaxies by measuring the inclination-dependence of optical colours for 24,276 well-resolved SDSS galaxies visually classified in Galaxy Zoo. We find clear trends of reddening with inclination which imply a
total extinction from face-on to edge-on of 0.7, 0.6, 0.5 and 0.4 magnitudes for the ugri passbands. We split the sample into bulgy (early-type) and disky (late-type) spirals using the SDSS fracdeV (or f_DeV) parameter and show that the average face-on colour of bulgy spirals is redder than the average edge-on colour of disky spirals. This shows that the observed optical colour of a spiral galaxy is determined almost equally by the spiral type (via the bulge-disk ratio and stellar populations), and reddening due to dust. We find that both luminosity and spiral type affect the total amount of extinction, with disky spirals at M_r ~ -21.5 mags having the most reddening. This decrease of reddening for the most luminous spirals has not been observed before and may be related to their lower levels of recent star formation. We compare our results with the latest dust attenuation models of Tuffs et al. We find that the model reproduces the observed trends reasonably well but overpredicts the amount of u-band attenuation in edge-on galaxies. We end by discussing the effects of dust on large galaxy surveys and emphasize that these effects will become important as we push to higher precision measurements of galaxy properties and their clustering.
We have identified a new class of galaxy cluster using data from the Galaxy Zoo project. These clusters are rare, and thus have apparently gone unnoticed before, despite their unusual properties. They appear especially anomalous when the morphologica
l properties of their component galaxies are considered. Their identification therefore depends upon the visual inspection of large numbers of galaxies, a feat which has only recently been made possible by Galaxy Zoo, together with the Sloan Digital Sky Survey. We present the basic properties of our cluster sample, and discuss possible formation scenarios and implications for cosmology.
We study the spectroscopic properties and environments of red spiral galaxies found by the Galaxy Zoo project. By carefully selecting face-on, disk dominated spirals we construct a sample of truly passive disks (not dust reddened, nor dominated by ol
d stellar populations in a bulge). As such, our red spirals represent an interesting set of possible transition objects between normal blue spirals and red early types. We use SDSS data to investigate the physical processes which could have turned these objects red without disturbing their morphology. Red spirals prefer intermediate density regimes, however there are no obvious correlations between red spiral properties and environment - environment alone is not sufficient to determine if a spiral will become red. Red spirals are a small fraction of spirals at low masses, but are a significant fraction at large stellar masses - massive galaxies are red independent of morphology. We confirm that red spirals have older stellar popns and less recent star formation than the main spiral population. While the presence of spiral arms suggests that major star formation cannot have ceased long ago, we show that these are not recent post-starbursts, so star formation must have ceased gradually. Intriguingly, red spirals are ~4 times more likely than normal spirals to host optically identified Seyfert or LINER, with most of the difference coming from LINERs. We find a curiously large bar fraction in the red spirals suggesting that the cessation of star formation and bar instabilities are strongly correlated. We conclude by discussing the possible origins. We suggest they may represent the very oldest spiral galaxies which have already used up their reserves of gas - probably aided by strangulation, and perhaps bar instabilities moving material around in the disk.
Several observational works have attempted to isolate the effects of galaxy interactions by comparing galaxies in pairs with isolated galaxies. However, different authors have proposed different ways to build these so-called control samples (CS). B
y using mock galaxy catalogues of the SDSS-DR4 built up from the Millennium Simulation, we explore how the way of building a CS might introduce biases which could affect the interpretation of results. We make use of the fact that the physics of interactions is not included in the semianalytic model, to infer that any difference between the mock control and pair samples can be ascribed to selection biases. Thus, we find that galaxies in pairs artificially tend to be older and more bulge-dominated, and to have less cold gas and different metallicities than their isolated counterparts. Also because of a biased selection, galaxies in pairs tend to live in higher density environments, and in haloes of larger masses. We find that imposing constraints on redshift, stellar masses and local densities diminishes the selection biases by ~70%. Based on these findings, we suggest observers how to build an unique and unbiased CS in order to reveal the effect of galaxy interactions.
This paper presents the first results from a new citizen science project: Galaxy Zoo Supernovae. This proof of concept project uses members of the public to identify supernova candidates from the latest generation of wide-field imaging transient surv
eys. We describe the Galaxy Zoo Supernovae operations and scoring model, and demonstrate the effectiveness of this novel method using imaging data and transients from the Palomar Transient Factory (PTF). We examine the results collected over the period April-July 2010, during which nearly 14,000 supernova candidates from PTF were classified by more than 2,500 individuals within a few hours of data collection. We compare the transients selected by the citizen scientists to those identified by experienced PTF scanners, and find the agreement to be remarkable - Galaxy Zoo Supernovae performs comparably to the PTF scanners, and identified as transients 93% of the ~130 spectroscopically confirmed SNe that PTF located during the trial period (with no false positive identifications). Further analysis shows that only a small fraction of the lowest signal-to-noise SN detections (r > 19.5) are given low scores: Galaxy Zoo Supernovae correctly identifies all SNe with > 8{sigma} detections in the PTF imaging data. The Galaxy Zoo Supernovae project has direct applicability to future transient searches such as the Large Synoptic Survey Telescope, by both rapidly identifying candidate transient events, and via the training and improvement of existing machine classifier algorithms.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
