Implications of Increased Central Mass Surface Densities for the Quenching of Low-mass Galaxies

ABSTRACT How do galaxy properties (such as stellar mass, luminosity, star formation rate, and morphology) and their evolution depend on the mass of their host dark matter halo? Using the Galaxy and Mass Assembly group catalogue, we address this question by exploring the dependence on host halo mass of the luminosity function (LF) and stellar mass function (SMF) for grouped galaxies subdivided by colour, morphology, and central/satellite. We find that spheroidal galaxies in particular dominate the bright and massive ends of the LF and SMF, respectively. More massive haloes host more massive and more luminous central galaxies. The satellites LF and SMF, respectively, show a systematic brightening of characteristic magnitude, and increase in characteristic mass, with increasing halo mass. In contrast to some previous results, the faint-end and low-mass slopes show little systematic dependence on halo mass. Semi-analytic models and simulations show similar or enhanced dependence of central mass and luminosity on halo mass. Faint and low-mass simulated satellite galaxies are remarkably independent of halo mass, but the most massive satellites are more common in more massive groups. In the first investigation of low-redshift LF and SMF evolution in group environments, we find that the red/blue ratio of galaxies in groups has increased since redshift z ≈ 0.3 relative to the field population. This observation strongly suggests that quenching of star formation in galaxies as they are accreted into galaxy groups is a significant and ongoing process.

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The reports of thick discs’ deaths are greatly exaggerated

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731415 ◽

2018 ◽

Vol 610 ◽

pp. A5 ◽

Cited By ~ 18

Author(s):

S. Comerón ◽

H. Salo ◽

J. H. Knapen

Keyword(s):

Point Spread Function ◽

Surface Brightness ◽

Scattered Light ◽

Stellar Structure ◽

High Mass ◽

Central Mass ◽

Thin Disc ◽

Point Spread ◽

Spread Function ◽

Low Mass

Recent studies have made the community aware of the importance of accounting for scattered light when examining low-surface-brightness galaxy features such as thick discs. In our past studies of the thick discs of edge-on galaxies in the Spitzer Survey of Stellar Structure in Galaxies – the S4G – we modelled the point spread function as a Gaussian. In this paper we re-examine our results using a revised point spread function model that accounts for extended wings out to more than 2 .́ 5. We study the 3.6 μm images of 141 edge-on galaxies from the S4G and its early-type galaxy extension. Thus, we more than double the samples examined in our past studies. We decompose the surface-brightness profiles of the galaxies perpendicular to their mid-planes assuming that discs are made of two stellar discs in hydrostatic equilibrium. We decompose the axial surface-brightness profiles of galaxies to model the central mass concentration – described by a Sérsic function – and the disc – described by a broken exponential disc seen edge-on. Our improved treatment fully confirms the ubiquitous occurrence of thick discs. The main difference between our current fits and those presented in our previous papers is that now the scattered light from the thin disc dominates the surface brightness at levels below μ ~ 26 mag arcsec-2. We stress that those extended thin disc tails are not physical, but pure scattered light. This change, however, does not drastically affect any of our previously presented results: 1) Thick discs are nearly ubiquitous. They are not an artefact caused by scattered light as has been suggested elsewhere. 2) Thick discs have masses comparable to those of thin discs in low-mass galaxies – with circular velocities vc< 120 km s-1 – whereas they are typically less massive than the thin discs in high-mass galaxies. 3) Thick discs and central mass concentrations seem to have formed at the same epoch from a common material reservoir. 4) Approximately 50% of the up-bending breaks in face-on galaxies are caused by the superposition of a thin and a thick disc where the scale-length of the latter is the largest.

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Rapid Profile Variations in the Broad Hα Line of the Seyfert Galaxy Markarian 6: Possible Evidence for Turbulence in the Accretion Disk

International Astronomical Union Colloquium ◽

10.1017/s025292110003102x ◽

2002 ◽

Vol 184 ◽

pp. 359-360

Author(s):

N. S. Asatrian ◽

E. Ye. Khachikian ◽

P. Notni

Keyword(s):

Seyfert Galaxy ◽

Difference Spectrum ◽

Radial Velocities ◽

Algebraic Equations ◽

Difference Spectra ◽

Central Mass ◽

Orbital Parameters ◽

Inclination Angles ◽

Low Mass ◽

The Difference

We report on implications for the geometrical and kinematic parameters of BLR gas on the basis of short timescale variability in the broad Hα profile shape. Data on rapid variations have been obtained at the 2.6−m telescope of the BAO (Asatrian, Khachikian & Notni, 1999). To search for variations in the profile, difference spectra (second minus first epoch) were examined. We believe that the structure of the underlying stellar continuum and the atmospheric features do not affect significantly the Hα difference profiles of Mark 6. Variations occurred simultaneously on the blue and red sides of Hα on a time scale of ≃ 50.7 minutes and take the form of three narrow, positive small bumps on each side in the difference spectrum. The positions of the bumps are −4400, −3100, −1700 and +1900, +4200 and +6600 kms−1. These changes may indicate the response of circularly rotating emitting gas at three orbits to a light pulse from a central source. In this case the pairs of blue and red bumps observed at −4400 and +6600, −3100 and +4200, and −1700 and 1900 km s−1 are formed in two opposite zones of gas close to the line of nodes. On the assumption that these orbits lie around a central massive object, orbital parameters (radii, velocities and inclination angles of orbital planes) of the clouds and the central mass can be found. The shift of each bump is defined by the combination of the relativistic Doppler effect due to the Keplerian orbital motion and the gravitational redshift. The six observed radial velocities are determined by six parameters: the orbital radii, R1, R2, R3 (or velocities, Vi, V2, V3) and the inclination angles i1, i2, i3 of the rotation planes. Thus, the expressions for the radial velocities form a system of six algebraic equations with six unknowns and can be solved. Using the difference of the orbital radii in absolute units (R3 − R1 = Δt C, where ΔtC, ≃ 50.7 minutes and C is the speed of light) we can derive the central mass M. Analytical solution gives: Error limits for the results are determined by the uncertainty of the input radial velocities, 300 km s−1. However, the value of the mass obtained is smaller by two orders of magnitude than the estimate for the dynamical mass of the nucleus of Mark 6 (M = 1 × 107M⊙ Dibai 1984). Such a low mass is excluded, therefore.

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Detection of Enhanced Central Mass-to-light Ratios in Low-mass Early-type Galaxies: Evidence for Black Holes?

The Astrophysical Journal ◽

10.3847/1538-4357/aa9021 ◽

2017 ◽

Vol 850 (1) ◽

pp. 15 ◽

Cited By ~ 7

Author(s):

Renuka Pechetti ◽

Anil Seth ◽

Michele Cappellari ◽

Richard McDermid ◽

Mark den Brok ◽

...

Keyword(s):

Black Holes ◽

Early Type ◽

Central Mass ◽

Low Mass

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VLA ammonia observations of L1287

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037895 ◽

2020 ◽

Vol 644 ◽

pp. A128

Author(s):

Inma Sepúlveda ◽

Robert Estalella ◽

Guillem Anglada ◽

Rosario López ◽

Angels Riera ◽

...

Keyword(s):

Unit Length ◽

Rotation Velocity ◽

Young Stellar Objects ◽

Central Mass ◽

Stellar Objects ◽

Molecular Outflow ◽

Velocity Gradients ◽

Low Mass ◽

Fu Ori ◽

High Level

Aims. In this paper, we study the dense gas of the molecular cloud LDN 1287 (L1287), which harbors a double FU Ori system, an energetic molecular outflow, and a still-forming cluster of deeply embedded low-mass young stellar objects that show a high level of fragmentation. Methods. We present optical Hα and [SII], and VLA NH3 (1, 1) and (2, 2) observations with an angular resolution of ~3′′.5. The observed NH3 spectra have been analyzed with the Hyperfine Structure tool, fitting simultaneously three different velocity components. Results. The NH3 emission from L1287 comes from four different structures: a core associated with RNO 1, a guitar-shaped core (the Guitar) and two interlaced filaments (the blue and red filaments) roughly centered toward the binary FU Ori system RNO 1B/1C and its associated cluster. Regarding the Guitar core, there are clear signatures of gas infall onto a central mass that has been estimated to be ~2.1M⊙. Regarding the two filaments, they have radii of ~0.03 pc, masses per unit length of ~50M⊙ pc−1, and are in near isothermal equilibrium. A central cavity is identified, probably related with the outflow and also revealed by the Hα and [SII] emission, with several young stellar objects near its inner walls. Both filaments show clear signs of perturbation by the high-velocity gas of the outflows driven by one or several young stellar objects of the cluster. The blue and red filaments are coherent in velocity and have nearly subsonic gas motions, except at the position of the embedded sources. Velocity gradients across the blue filament can be interpreted either as infalling material onto the filament or rotation. Velocity gradients along the filaments are interpreted as infall motions toward a gravitational well at the intersection of the two filaments.

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Iron K-Line Emission from X-Ray Binaries

International Astronomical Union Colloquium ◽

10.1017/s0252921100107389 ◽

1988 ◽

Vol 102 ◽

pp. 47-50

Author(s):

K. Masai ◽

S. Hayakawa ◽

F. Nagase

Keyword(s):

Accretion Disk ◽

Radiative Recombination ◽

Characteristic Temperature ◽

Line Emission ◽

Ionization Front ◽

Continuum Radiation ◽

X Ray ◽

Low Mass ◽

X Ray Binaries

AbstractEmission mechanisms of the iron Kα-lines in X-ray binaries are discussed in relation with the characteristic temperature Txof continuum radiation thereof. The 6.7 keV line is ascribed to radiative recombination followed by cascades in a corona of ∼ 100 eV formed above the accretion disk. This mechanism is attained for Tx≲ 10 keV as observed for low mass X-ray binaries. The 6.4 keV line observed for binary X-ray pulsars with Tx> 10 keV is likely due to fluorescence outside the He II ionization front.

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