81 research outputs found
Host Galaxy Properties of CaII and NaI Quasar Absorption-Line Systems
Many questions remain within the areas of galaxy formation and evolution. Understanding the origin of gas in galaxy environments, whether as tidal debris, infalling High Velocity Clouds, galaxy outflows, or as gaseous material residing in galaxy disks, is an important step in answering those questions. Quasar absorption-lines can often be used to probe the environments of intervening galaxies. Traditionally, quasar absorption-lines are studied independently of the host galaxy but this method denies us the exploration of the connection between galaxy and environment. Instead, one can select pairs of known galaxies and quasars. This gives much more information regarding the host galaxy and allows us to better connect galaxy properties with associated absorbers.
We use the seventh data release of the Sloan Digital Sky Survey to generate a sample of spectroscopic galaxy-quasar pairs. We cross-correlated a sample of 105,000 quasars and ~800,000 galaxies to produce ~98,000 galaxy-quasar pairs, with the quasar projected within 100 kpc of the galaxy. Adopting an automated line-finding algorithm and using the galaxy redshift as a prior, we search through all quasar spectra and identify CaII and NaI absorption due to the intervening galaxy. This procedure produced 1745 Ca~II absorbers and 4500 NaI absorbers detected at or above 2-sigma. Stacking analysis of a subset of absorbers at z>0.01, with significances at or above 3-sigma, showed strong CaII and NaI features around external galaxies.
Using the same subset of absorbers at z>0.01, we looked for correlations between absorber and galaxy properties and examined differences in galaxy properties between the absorbers and non-absorbers. We found no correlations with absorber strength or differences between many galaxy properties at the 3-sigma level. The lack of correlations and differences between absorbers and non-absorbers suggest a ubiquitous nature for CaII and NaI around all types of galaxies, with the absorbers showing no geometric preference within galaxy halos. This suggests a possible origin as leftover debris from past mergers that has been redistributed within the halo over time.
The main results are presented in Chapters 3 and 4, with complimentary work presented in Chapter 5
SDSS-IV MaNGA: Modeling the Spectral Line Spread Function to Sub-Percent Accuracy
The SDSS-IV Mapping Nearby Galaxies at APO (MaNGA) program has been operating
from 2014-2020, and has now observed a sample of 9,269 galaxies in the low
redshift universe (z ~ 0.05) with integral-field spectroscopy. With
rest-optical (\lambda\lambda 0.36 - 1.0 um) spectral resolution R ~ 2000 the
instrumental spectral line-spread function (LSF) typically has 1sigma width of
about 70 km/s, which poses a challenge for the study of the typically 20-30
km/s velocity dispersion of the ionized gas in present-day disk galaxies. In
this contribution, we present a major revision of the MaNGA data pipeline
architecture, focusing particularly on a variety of factors impacting the
effective LSF (e.g., undersampling, spectral rectification, and data cube
construction). Through comparison with external assessments of the MaNGA data
provided by substantially higher-resolution R ~ 10,000 instruments we
demonstrate that the revised MPL-10 pipeline measures the instrumental line
spread function sufficiently accurately (<= 0.6% systematic, 2% random around
the wavelength of Halpha) that it enables reliable measurements of
astrophysical velocity dispersions sigma_Halpha ~ 20 km/s for spaxels with
emission lines detected at SNR > 50. Velocity dispersions derived from [O II],
Hbeta, [O III], [N II], and [S II] are consistent with those derived from
Halpha to within about 2% at sigma_Halpha > 30 km/s. Although the impact of
these changes to the estimated LSF will be minimal at velocity dispersions
greater than about 100 km/s, scientific results from previous data releases
that are based on dispersions far below the instrumental resolution should be
reevaulated.Comment: 26 pages, 23 figures. Accepted for publication in A
P-MaNGA : full spectral fitting and stellar population maps from prototype observations
MC acknowledges support from a Royal Society University Research Fellowship.MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) is a 6-yearSDSS-IV survey that will obtain resolved spectroscopy from 3600 Å to10300 Å for a representative sample of over 10,000 nearby galaxies.In this paper, we derive spatially resolved stellar population properties and radial gradients by performing full spectral fitting of observed galaxy spectra from P-MaNGA, a prototype of the MaNGA instrument. These data include spectra for eighteen galaxies, covering a large range of morphological type. We derive age, metallicity, dust and stellar mass maps, and their radial gradients, using high spectral-resolution stellar population models, and assess the impact of varying the stellar library input to the models. We introduce a method to determine dust extinction which is able to give smooth stellar mass maps even in cases of high and spatially non-uniform dust attenuation.With the spectral fitting we produce detailed maps of stellar population properties which allow us to identify galactic features among this diverse sample such as spiral structure, smooth radial profiles with little azimuthal structure in spheroidal galaxies, and spatially distinct galaxy sub-components. In agreement with the literature, we find the gradients for galaxies identified as early-type to be on average flat in age, and negative (- 0.15 dex / Re ) in metallicity,whereas the gradients for late-type galaxies are on average negative in age (- 0.39 dex / Re ) and flat in metallicity. We demonstrate howdifferent levels of data quality change the precision with which radialgradients can be measured. We show how this analysis, extended to thelarge numbers of MaNGA galaxies, will have the potential to shed lighton galaxy structure and evolution.PostprintPeer reviewe
SDSS-IV MaNGA: the spectroscopic discovery of strongly lensed galaxies
We present a catalogue of 38 spectroscopically detected strong galaxy–galaxy gravitational lens candidates identified in the Sloan Digital Sky Survey IV (SDSS-IV). We were able to simulate narrow-band images for eight of them demonstrating evidence of multiple images. Two of our systems are compound lens candidates, each with two background source-planes. One of these compound systems shows clear lensing features in the narrow-band image. Our sample is based on 2812 galaxies observed by the Mapping Nearby Galaxies at APO (MaNGA) integral field unit (IFU). This Spectroscopic Identification of Lensing Objects (SILO) survey extends the methodology of the Sloan Lens ACS Survey (SLACS) and BOSS Emission-Line Survey (BELLS) to lower redshift and multiple IFU spectra. We searched ∼1.5 million spectra, of which 3065 contained multiple high signal-to-noise ratio background emission-lines or a resolved [O ii] doublet, that are included in this catalogue. Upon manual inspection, we discovered regions with multiple spectra containing background emission-lines at the same redshift, providing evidence of a common source-plane geometry which was not possible in previous SLACS and BELLS discovery programs. We estimate more than half of our candidates have an Einstein radius ≳ 1.7 arcsec, which is significantly greater than seen in SLACS and BELLS. These larger Einstein radii produce more extended images of the background galaxy increasing the probability that a background emission-line will enter one of the IFU spectroscopic fibres, making detection more likely
Galaxies in front of Quasars: Mrk 1456 and SDSS J114719.90+522923.2
The chance projection of the disk of Mrk~1456 onto a background QSO is
similar to the case of SBS 1543+593/HS 1543+5921. Mrk~1456 is a luminous,
late-type spiral at z ~ 0.05. Though the QSO, SDSS J114719.90+522923.2 at z ~
2, has not yet been observed with ultraviolet spectroscopy, it shows strong Ca
II absorption at the redshift of Mrk 1456 which gives evidence that it is a
possible Damped Lyman Alpha absorber. Spectroscopy of the star-forming nucleus
of Mrk~1456 allows us to apply emission-line diagnostics to infer the chemical
abundances at the center of the galaxy, and to make a prediction of the
expected metallicity on the sightline to the QSO.Comment: 23 pages, 4 figures, accepted for publication in A
Galaxy Zoo : 3D – crowdsourced bar, spiral, and foreground star masks for MaNGA target galaxies
Funding: Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science, and the Participating Institutions. We gratefully acknowledge the National Science Foundation’s support of the Keck Northeast Astronomy Consortium’s REU program through grants AST-1005024 and AST-1950797, the KINSC (Koshland Integrated Natural Sciences Centre) at Haverford College for Summer Scholar funding, and the Ogden Trust, UK for support for summer undergraduate internships.The challenge of consistent identification of internal structure in galaxies – in particular disc galaxy components like spiral arms, bars, and bulges – has hindered our ability to study the physical impact of such structure across large samples. In this paper we present Galaxy Zoo: 3D (GZ:3D) a crowdsourcing project built on the Zooniverse platform that we used to create spatial pixel (spaxel) maps that identify galaxy centres, foreground stars, galactic bars, and spiral arms for 29 831 galaxies that were potential targets of the MaNGA survey (Mapping Nearby Galaxies at Apache Point Observatory, part of the fourth phase of the Sloan Digital Sky Surveys or SDSS-IV), including nearly all of the 10 010 galaxies ultimately observed. Our crowdsourced visual identification of asymmetric internal structures provides valuable insight on the evolutionary role of non-axisymmetric processes that is otherwise lost when MaNGA data cubes are azimuthally averaged. We present the publicly available GZ:3D catalogue alongside validation tests and example use cases. These data may in the future provide a useful training set for automated identification of spiral arm features. As an illustration, we use the spiral masks in a sample of 825 galaxies to measure the enhancement of star formation spatially linked to spiral arms, which we measure to be a factor of three over the background disc, and how this enhancement increases with radius.Publisher PDFPeer reviewe
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