300 research outputs found
The sloan digital sky survey reverberation mapping project : ensemble spectroscopic variability of quasar broad emission lines
No full textM.Y.S. acknowledges support from the China Scholarship Council (No. [2013]3009). J.R.T. and Y.S. acknowledge support from NASA through Hubble Fellowship grants #51330 and #51314, respectively, awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA under contract NAS 5-26555. W.N.B. acknowledges support from NSF grant AST-1108604 and the V. M. Willaman Endowment. KDD is supported by an NSF AAPF fellowship awarded under NSF grant AST-1302093.We explore the variability of quasars in the Mg ii and Hβ broad emission lines and ultraviolet/optical continuum emission using the Sloan Digital Sky Survey Reverberation Mapping project (SDSS-RM). This is the largest spectroscopic study of quasar variability to date: our study includes 29 spectroscopic epochs from SDSS-RM over 6 months, containing 357 quasars with Mg ii and 41 quasars with Hβ . On longer timescales, the study is also supplemented with two-epoch data from SDSS-I/II. The SDSS-I/II data include an additional 2854 quasars with Mg ii and 572 quasars with Hβ . The Mg ii emission line is significantly variable (Δƒ/ƒ ~ 10% on ~100-day timescales), a necessary prerequisite for its use for reverberation mapping studies. The data also confirm that continuum variability increases with timescale and decreases with luminosity, and the continuum light curves are consistent with a damped random-walk model on rest-frame timescales of ≳5 days. We compare the emission-line and continuum variability to investigate the structure of the broad-line region. Broad-line variability shows a shallower increase with timescale compared to the continuum emission, demonstrating that the broad-line transfer function is not a δ-function. Hβ is more variable than Mg ii (roughly by a factor of ~1.5), suggesting different excitation mechanisms, optical depths and/or geometrical configuration for each emission line. The ensemble spectroscopic variability measurements enabled by the SDSS-RM project have important consequences for future studies of reverberation mapping and black hole mass estimation of 1<픃<2 quasars.Peer reviewe
The impact of merging on the origin of kinematically misaligned and counter-rotating galaxies in MaNGA
No full textGalaxy mergers and interactions are expected to play a significant role leading to offsets between gas and stellar motions in galaxies. Herein, we cross-match galaxies in Mapping Nearby Galaxies at Apache Point Observatory MPL-8 with the Dark Energy Spectroscopic Instrument Legacy Surveys and identify 311 merging galaxies that have reliable measurements of ΔPA, the difference between the stellar and gas kinematic position angles, to investigate the impacts of merging on gas–stellar rotation misalignments. We find that the merging fractions of misaligned galaxies (30∘⩽ΔPA < 150○) are higher than those of co-rotators (ΔPA < 30○) in both quiescent and star-forming galaxies. This result suggests that merging is one process to produce kinematic misalignments. The merging fraction of counter-rotators (ΔPA ≥ 150○) is lower than that of misaligned galaxies in both quiescent and star-forming galaxies, while in the latter it is likely even lower than that of co-rotators. The orbital angular momentum transfer to the spins of stars and gas during merging and the tidal feature disappearance can lead to small merging fractions in counter-rotators. Numerous new stars that inherit angular momentum from gas after merging can further lower the merging fraction of star-forming counter-rotators
Surface photometry of LSB edge-on galaxies
No full textABSTRACT We present results of surface photometry for eleven edge-on galaxies observed with the 6-m telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences. The photometric scale length, the scale height, and the central surface brightness of the stellar disks for the galaxies were found using photometric cuts made parallel to the major and the minor axes for each galaxy. We show that four galaxies in our sample that were visually classified as objects of lowest surface brightness in the Revised Flat Galaxies Catalog have LSB (low surface brightness) disks. Stellar disks of our LSB galaxies are thinner than HSB (high surface brightness) ones. There is a good correlation between the central surface brightness of the stellar disk and its ratio of vertical to radial scales. The ratio of the disk photometric scales enables us to estimate the mass of the spherical galactic subsystem using results from numerical modeling. Combining our results with published rotation curves we determined the mass of dark halos for the galaxies in our sample. The LSB galaxies tend to harbor relatively more massive spherical subsystems than those of HSB's. Indeed, we found no systematic difference between our LSB and HSB objects in dark halo masses considering it separately from the bulge. At the same time, the inferred mass/luminosity ratio for the LSB disks appears to be systematically higher, when compared to the ratio for HSB ones
SDSS-IV MaNGA: Ionization sources of diffuse extra-planar galactic medium
No full textWe explore sources of ionization of diffuse gas at different altitudes in
galaxies in dependence of their stellar mass, \Ha\ luminosity, and specific
star formation rate. We use the MaNGA data from SDSS-IV data release DR16
together with photoionization and shock ionization models provided by the 3MdB
database. Our sample comprises 239 edge-on galaxies, which makes our results
statistically valuable. We reach very high galactic altitudes with the help of
spectra stacking. We demonstrate that models of the gas photoionization in a
combination of young OB-stars and hot low-mass evolved stars (HOLMES) describes
the gas ionization state in the galaxies of all types on diagnostic diagrams.
Nevertheless, the shock waves may contribute to the gas ionization in massive
galaxies with passive star formation. We observe a general trend of decreasing
the fraction of the ionizing flux from OB-stars and the ionization parameter
with the altitude, while the role of the ionization by the HOLMES increases.
The biggest difference in the contribution from these types of ionizing sources
correlates with the specific star formation rate and with stellar masses of
galaxies. The HOLMES are the principal gas ionization sources in massive
galaxies with passive star formation, while OB-stars dominate the gas
ionization in low-mass galaxies with active star formation.Comment: 14 pages, 9 figures. Published in Astronomy Letter
SDSS-IV MaNGA : 3D spin alignment of spiral and S0 galaxies
No full textWe investigate the 3D spin alignment of galaxies with respect to the large-scale filaments using the MaNGA survey. The cosmic web is reconstructed from the Sloan Digital Sky Survey using DisPerSE and the 3D spins of MaNGA galaxies are estimated using the thin disk approximation with integral field spectroscopy kinematics. Late-type spiral galaxies are found to have their spins parallel to the closest filament’s axis. The alignment signal is found to be dominated by low-mass spirals. Spins of S0-type galaxies tend to be oriented preferentially in perpendicular direction with respect to the filament’s axis. This orthogonal orientation is found to be dominated by S0s that show a notable misalignment between their kinematic components of stellar and ionised gas velocity fields and/or by low mass S0s with lower rotation support compared to their high mass counterparts. Qualitatively similar results are obtained when splitting galaxies based on the degree of ordered stellar rotation, such that galaxies with high spin magnitude have their spin aligned, and those with low spin magnitude in perpendicular direction to the filaments. In the context of conditional tidal torque theory, these findings suggest that galaxies’ spins retain memory of their larger-scale environment. In agreement with measurements from hydrodynamical cosmological simulations, the measured signal at low redshift is weak, yet statistically significant. The dependence of the spin-filament orientation of galaxies on their stellar mass, morphology and kinematics highlights the importance of sample selection to detect the signal.Peer reviewe
The Reliability of Galaxy Classifications by Citizen Scientists
No full textCitizen scientists are becoming more and more important in helping professionals working through big data. An example in astronomy is crowdsourced galaxy classification. But how reliable are these classifications for studies of galaxy evolution? We present a tool in order to investigate those morphological classifications and test it on a diverse population on our campus. We observe a slight offset towards earlier Hubble types in the crowdsourced morphologies, when compared to professional classifications
THE SPACE INTERFEROMETRY MISSION ASTROMETRIC GRID GIANT STAR SURVEY. III. BASIC STELLAR PARAMETERS FOR AN EXTENDED SAMPLE
No full textSDSS. IV. MaNGA: The Impact of the Acquisition of Gas with Opposite Angular Momentum on the Evolution of Galaxies
No full textA gaseous counterrotating galaxy is a galaxy containing a gas component with opposite angular momentum to the main stellar disk. The counterrotating gas provides direct evidence for the accretion of external material, a key aspect in hierarchical galaxy evolution. We identified 303 gaseous counterrotators out of 9992 galaxies in MaNGA. The majority of the counterrotators are early types. This implies their formation is highly correlated with early-type galaxies, although it is still difficult to know if one leads to the other. To disentangle which of the galaxy characteristics within a morphological class were changed by the accretion of counterrotating gas, we carefully selected a comparison sample with similar fundamental galactic properties but corotation in gas. This comparison shows that gaseous counterrotation correlates with weak rotation in the stellar component, the high central concentration of star-forming regions, if present, and a higher fraction of central low ionization emission regions (cLIER) galaxies. The light distributions of the stellar components, dust and H i content (both low), and overall suppressed star formation rates are similar for both samples and seem typical for the morphological class. We claim that elliptical and about half of the lenticular counterrotators, those with weak rotation in the stellar component in the outskirts and central regions, likely have a major merger origin for the gas acquisition, and the other half of lenticulars, with stronger stellar rotation, may have a minor merger or pure gas accretion origin
Magnetic-force microscopy for investigation of metal nanowires obtained by replication of pores of polymer track membranes / D.A. Bizyaev, A.A. Bukharaev, Sergey Bedin, Dmitry Zagorskiy, Ilia Doludenko
No full textСекция 4. Пучковые методы формирования наноматериалов и наноструктурОдно из применений радиационных технологий - получение трековых мембран - пористых полимерных матриц. Поровая структура таких матриц может направленно изменяться и использоваться для задач т.н. матричного синтеза. В работе методом матричного синтеза на основе полимерной трековой мембраны были получены нанопроволоки из железа и никеля. Магнитно-силовая микроскопия (МСМ) применялась для визуализации этих проволок, находящихся в ростовой матрице. Исследована зависимость характера МСМ изображения от расположения нанопроволок внутри ростовой матрицы и от ориентации внешнего магнитного поля = The obtaining of track membranes is one of the applications of radiation technologies. Porous structure of such membranes could be changed by will and could be used for matrix synthesis. Matrix synthesis based on specially prepared porous matrixes was used in this work for obtaining of nanowires of Iron and Nickel. Magnetic –force microscopy was applied for fro visualization of these nanowires embedded in host matrix. The dependence of magnetic-force images of nanowires position inside matrix and on orientation of external magnetic field was investigate
Magnetic-force microscopy for investigation of metal nanowires obtained by replication of pores of polymer track membranes / D.A. Bizyaev, A.A. Bukharaev, Sergey Bedin, Dmitry Zagorskiy, Ilia Doludenko
No full textСекция 4. Пучковые методы формирования наноматериалов и наноструктурОдно из применений радиационных технологий - получение трековых мембран - пористых полимерных матриц. Поровая структура таких матриц может направленно изменяться и использоваться для задач т.н. матричного синтеза. В работе методом матричного синтеза на основе полимерной трековой мембраны были получены нанопроволоки из железа и никеля. Магнитно-силовая микроскопия (МСМ) применялась для визуализации этих проволок, находящихся в ростовой матрице. Исследована зависимость характера МСМ изображения от расположения нанопроволок внутри ростовой матрицы и от ориентации внешнего магнитного поля = The obtaining of track membranes is one of the applications of radiation technologies. Porous structure of such membranes could be changed by will and could be used for matrix synthesis. Matrix synthesis based on specially prepared porous matrixes was used in this work for obtaining of nanowires of Iron and Nickel. Magnetic –force microscopy was applied for fro visualization of these nanowires embedded in host matrix. The dependence of magnetic-force images of nanowires position inside matrix and on orientation of external magnetic field was investigate
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