Percentage Of Galaxies Research Articles

The miniJPAS survey

The miniJPAS survey has observed ∼1 deg2 of the AEGIS field with 60 bands (spectral resolution of R ∼ 60) in order to demonstrate the scientific potential of the Javalambre-Physics of the Accelerating Universe Astrophysical Survey (J-PAS), which will map ∼8000 deg2 of the northern sky over the coming years. In particular, this paper demonstrates the potential of J-PAS in detecting groups with mass of up to 1013 M⊙ and in characterising their galaxy populations up to z ∼ 1. The parametric code BaySeAGal is used to derive the stellar population properties by fitting the J-PAS spectral energy distribution (SED) of the galaxy members in 80 groups at z ≤ 0.8 previously detected by the AMICO code, and of a galaxy field sample retrieved from the whole miniJPAS down to r < 22.75 (AB). Blue, red, quiescent, and transition (blue quiescent or green valley) galaxy populations are identified through their rest-frame (extinction-corrected) (u − r)int colour, galaxy stellar mass (M⋆), and specific star formation rate (sSFR). We measure the abundance of these galaxies as a function of M⋆ and environment in order to investigate the role that groups play in quenching star formation. Our findings are as follows. (i) The fraction of red and quiescent galaxies in groups increases with M⋆ and is always higher in groups (28% on average) than in the field (5%). (ii) The quenched fraction excess (QFE) in groups shows a strong dependence on M⋆, and increases from a few percent for galaxies with M⋆ < 1010 M⊙ to higher than 60% for galaxies with M⋆ > 3 × 1011 M⊙. (iii) The abundance excess of transition galaxies in groups shows a modest dependence on M⋆, being 5%–10% for galaxies with M⋆ < 1011 M⊙. (iv) The fading timescale, defined as the time that galaxies in groups spend in the transition phase, is very short (< 1.5 Gyr), indicating that the star formation of galaxies in groups declines very rapidly. (v) The evolution of the galaxy quenching rate in groups shows a modest but significant evolution since z ∼ 0.8. This latter result is compatible with the expected evolution with constant QFE = 0.4, which has been previously measured for satellites in the nearby Universe, as traced by SDSS. Further, this evolution is consistent with a scenario where the low-mass star forming galaxies in clusters at z = 1–1.4 are environmentally quenched, as previously reported by other surveys.

Identifying and Repairing Catastrophic Errors in Galaxy Properties Using Dimensionality Reduction

Abstract Our understanding of galaxy evolution is derived from large surveys designed to maximize efficiency by only observing the minimum amount needed to infer properties for a typical galaxy. However, for a few percent of galaxies in every survey, these observations are insufficient and derived properties can be catastrophically wrong. Further, it is currently difficult or impossible to determine which objects have failed, so that these contaminate every study of galaxy properties. We develop a novel method to identify these objects by combining the astronomical codes that infer galaxy properties with the dimensionality reduction algorithm t-SNE, which groups similar objects to determine which inferred properties are out of place. This method provides an improvement for the COSMOS catalog, which already uses existing techniques for catastrophic error removal, and therefore should improve the quality of large catalogs and any studies that are sensitive to large redshift errors.

Photometric Redshifts of Emission-line Galaxies Using Ramp Filters

Abstract Broadband photometric redshifts are routinely obtained for galaxies to estimate their distances. While effective for many uses, the common resolution in z of 0.01–0.02 is too coarse for detailed large-scale structure mapping, particularly in low-density volumes where the galaxy distribution is least understood. To map galaxies in these low-density volumes, and noting that the percentage of galaxies having emission tends to rise as number density decreases, we have designed a filter system to photometrically measure the redshifts of galaxies with emission. The system consists of two “ramp” filters that cover a common wavelength range with transmission curves sloping from blue to red and from red to blue respectively. This causes the intensity of the image through either filter to be a function of the wavelength of the emission line. A third filter with a bandpass to the side is used to measure and remove the continuum. We have obtained a set of such filters that are tuned for isolating Hα in the redshift range of 3,000–9,000 km s−1. Simulated photometry, applied to spectra of 197 emission-line galaxies from the SDSS, shows the accuracy of the method to be between 250 and 620 km s−1, depending on line strength. Actual photometry of a sample of 16 active galaxies measured their redshifts with an accuracy of 573 km s−1. This is approximately an order of magnitude more accurate than broadband photometric redshifts. We discuss the errors inherent in this method and present ways to modify the filter set to further improve accuracy.

The origin of diverse α-element abundances in galaxy discs

Spectroscopic surveys of the Galaxy reveal that its disc stars exhibit a spread in $\mathrm{[\alpha/Fe]}$ at fixed $\mathrm{[Fe/H]}$, manifest at some locations as a bimodality. The origin of these diverse, and possibly distinct, stellar populations in the Galactic disc is not well understood. We examine the Fe and $\alpha$-element evolution of 133 Milky Way-like galaxies from the EAGLE simulation, to investigate the origin and diversity of their $\mathrm{[\alpha/Fe]}$-$\mathrm{[Fe/H]}$ distributions. We find that bimodal $\mathrm{[\alpha/Fe]}$ distributions arise in galaxies whose gas accretion histories exhibit episodes of significant infall at both early and late times, with the former fostering more intense star formation than the latter. The shorter characteristic consumption timescale of gas accreted in the earlier episode suppresses its enrichment with iron synthesised by Type Ia SNe, resulting in the formation of a high-$\mathrm{[\alpha/Fe]}$ sequence. We find that bimodality in $\mathrm{[\alpha/Fe]}$ similar to that seen in the Galaxy is rare, appearing in approximately 5 percent of galaxies in our sample. We posit that this is a consequence of an early gas accretion episode requiring the mass accretion history of a galaxy's dark matter halo to exhibit a phase of atypically-rapid growth at early epochs. The scarcity of EAGLE galaxies exhibiting distinct sequences in the $\mathrm{[\alpha/Fe]}$-$\mathrm{[Fe/H]}$ plane may therefore indicate that the Milky Way's elemental abundance patterns, and its accretion history, are not representative of the broader population of $\sim L^\star$ disc galaxies.

Z ∼ 2: An Epoch of Disk Assembly

Abstract We explore the evolution of the internal gas kinematics of star-forming galaxies from the peak of cosmic star formation at z ∼ 2 to today. Measurements of galaxy rotation velocity V rot, which quantify ordered motions, and gas velocity dispersion σ g , which quantify disordered motions, are adopted from the DEEP2 and SIGMA surveys. This sample covers a continuous baseline in redshift over 0.1 < z < 2.5 , spanning 10 Gyr. At low redshift, nearly all sufficiently massive star-forming galaxies are rotationally supported ( V rot > σ g ). By z = 2, 50% and 70% of galaxies are rotationally supported at low ( 10 9 – 10 10 M ⊙ ) and high ( 10 10 – 10 11 M ⊙ ) stellar mass, respectively. For V rot > 3 σ g , the percentage drops below 35% for all masses. From z = 2 to now, galaxies exhibit remarkably smooth kinematic evolution on average. All galaxies tend toward rotational support with time, and higher-mass systems reach it earlier. This is largely due to a mass-independent decline in σ g by a factor of 3 since z = 2. Over the same time period, V rot increases by a factor of 1.5 in low-mass systems but does not evolve at high mass. These trends in V rot and σ g are at a fixed stellar mass and therefore should not be interpreted as evolutionary tracks for galaxy populations. When populations are linked in time via abundance matching, σ g declines as before and V rot strongly increases with time for all galaxy populations, enhancing the evolution in V rot / σ g . These results indicate that z = 2 is a period of disk assembly, during which strong rotational support is only just beginning to emerge.

Means of confusion: how pixel noise affects shear estimates for weak gravitational lensing

Weak-lensing shear estimates show a troublesome dependence on the apparent brightness of the galaxies used to measure the ellipticity: In several studies, the amplitude of the inferred shear falls sharply with decreasing source significance. This dependence limits the overall ability of upcoming large weak-lensing surveys to constrain cosmological parameters. We seek to provide a concise overview of the impact of pixel noise on weak-lensing measurements, covering the entire path from noisy images to shear estimates. We show that there are at least three distinct layers, where pixel noise not only obscures but biases the outcome of the measurements: 1) the propagation of pixel noise to the non-linear observable ellipticity; 2) the response of the shape-measurement methods to limited amount of information extractable from noisy images; and 3) the reaction of shear estimation statistics to the presence of noise and outliers in the measured ellipticities. We identify and discuss several fundamental problems and show that each of them is able to introduce biases in the range of a few tenths to a few percent for galaxies with typical significance levels. Furthermore, all of these biases do not only depend on the brightness of galaxies but also on their ellipticity, with more elliptical galaxies often being harder to measure correctly. We also discuss existing possibilities to mitigate and novel ideas to avoid the biases induced by pixel noise. We present a new shear estimator that shows a more robust performance for noisy ellipticity samples. Finally, we release the open-source python code to predict and efficiently sample from the noisy ellipticity distribution and the shear estimators used in this work at https://github.com/pmelchior/epsnoise

Why are AGN found in high-mass galaxies?

We use semi-analytic models implemented in the Millennium Simulation to analyze the merging histories of dark matter haloes and of the galaxies that reside in them. We assume that supermassive black holes only exist in galaxies that have experienced at least one major merger. Only a few percent of galaxies with stellar masses less than $M_* < 10^{10} M_{\odot}$ are predicted to have experienced a major merger and to contain a black hole. The fraction of galaxies with black holes increases very steeply at larger stellar masses. This agrees well with the observed strong mass dependence of the fraction of nearby galaxies that contain either low-luminosity (LINER-type) or higher-luminosity (Seyfert or composite-type) AGN. We then investigate when the major mergers that first create the black holes are predicted to occur. High mass galaxies are predicted to have formed their black holes at very early epochs. The majority of low mass galaxies never experience a major merger and hence do not contain a black hole, but a significant fraction of the supermassive black holes that do exist in low mass galaxies are predicted to have formed recently.

Young Crab‐like Pulsars and Luminous X‐Ray Sources in Starbursts and Optically Dull Galaxies

Recent Chandra observations of nearby galaxies have revealed a number of ultraluminous X-ray sources (ULXs) with super-Eddington luminosities, away from the central regions of nonactive galaxies. The nature of these sources is still debated. We argue that a fraction of them could be young, Crab-like pulsars, the X-ray luminosity of which is powered by rotation. We use the pulsar birth parameters estimated from radio pulsar data to compute the steady state pulsar X-ray luminosity distribution as a function of the star formation rate (SFR) in the galaxy. We find that ~10% of optically dull galaxies are expected to have a source with LX 1039 ergs s-1, while starburst galaxies should each have several of these sources. We estimate that the X-ray luminosity of a few percent of galaxies is dominated by a single bright pulsar with LX 1039 ergs s-1, roughly independently of its SFR. We discuss observational diagnostics that can help distinguish the young pulsar population in ULXs.

A study of warm IRAS Seyfert galaxies

The properties of warm IRAS Seyfert galaxies, those with abnormally blue 25 micron to 60 micron flux ratios, are discussed. It is shown that more than 70 percent of galaxies with F(60)/F(25) of 3 or less for which optical spectroscopy is available are Seyfert galaxies and that most are of type 2. The newly discovered type 2 Seyferts have a space density comparable to known Markarian Seyfert galaxies but less than type 2 Seyferts in the CfA redshift survey. The 25 micron emission from most Seyferts appears to be dominated by their nuclei; the evidence indicates that Seyferts with steeply rising far-infrared spectra (cold Seyferts) are dominated by star-formation regions at 60 and 100 microns. Cold Seyferts are found to have significantly lower 25 micron luminosities. The nuclear optical emission-line ratios of cold type 2 Seyferts are intermediate between those of warm Seyferts and H II regions, suggesting that regions of massive star formation exist in the immediate vicinity of the nuclei. 26 references.