The host galaxies of active galactic nuclei Kauffmann, Guinevere; Heckman, Timothy M.; Tremonti, Christy ...
Monthly notices of the Royal Astronomical Society,
12/2003, Letnik:
346, Številka:
4
Journal Article
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We examine the properties of the host galaxies of 22 623 narrow-line active galactic nuclei (AGN) with 0.02 < z < 0.3 selected from a complete sample of 122 808 galaxies from the Sloan Digital Sky ...Survey. We focus on the luminosity of the O iiiλ5007 emission line as a tracer of the strength of activity in the nucleus. We study how AGN host properties compare with those of normal galaxies and how they depend on LO iii. We find that AGN of all luminosities reside almost exclusively in massive galaxies and have distributions of sizes, stellar surface mass densities and concentrations that are similar to those of ordinary early-type galaxies in our sample. The host galaxies of low-luminosity AGN have stellar populations similar to normal early types. The hosts of high-luminosity AGN have much younger mean stellar ages. The young stars are not preferentially located near the nucleus of the galaxy, but are spread out over scales of at least several kiloparsecs. A significant fraction of high-luminosity AGN have strong Hδ absorption-line equivalent widths, indicating that they experienced a burst of star formation in the recent past. We have also examined the stellar populations of the host galaxies of a sample of broad-line AGN. We conclude that there is no significant difference in stellar content between type 2 Seyfert hosts and quasars (QSOs) with the same O iii luminosity and redshift. This establishes that a young stellar population is a general property of AGN with high O iii luminosities.
THE CURRENT STAR FORMATION RATE OF K+A GALAXIES Nielsen, Danielle M; Ridgway, Susan E; De Propris, Roberto ...
Astrophysical journal. Letters,
12/2012, Letnik:
761, Številka:
2
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We derive the stacked 1.4 GHz flux from the FIRST survey for 811 K+A galaxies selected from the Sloan Digital Sky Survey Data Release 7. For these objects we find a mean flux density of 56 + or - 9 ...mu Jy. A similar stack of radio-quiet white dwarfs yields an upper limit of 43 mu Jy at a 5sigma significance to the flux in blank regions of the sky. This implies an average star formation rate of 1.6 + or - 0.3 M sub(middot in circle) yr super(-1) for K+A galaxies. However, the majority of the signal comes from ~4% of K+A fields that have aperture fluxes above the 5sigma noise level of the FIRST survey. A stack of the remaining galaxies shows little residual flux consistent with an upper limit on star formation of 1.3 M sub(middot in circle) yr super(-1). Even for a subset of 456 "young" (spectral ages <250 Myr) K+A galaxies, we find that the stacked 1.4 GHz flux is consistent with no current star formation. Our data suggest that the original starburst has been terminated in the majority of K+A galaxies, but that this may represent part of a duty cycle where a fraction of these galaxies may be active at a given moment with dusty starbursts and active galactic nuclei being present.
Type II quasars are luminous active galactic nuclei (AGNs) whose centers are obscured by large amounts of gas and dust. In this paper we present three-band Hubble Space Telescope images of nine type ...II quasars with redshifts 0.2 < z < 0.4 selected from the Sloan Digital Sky Survey based on their emission-line properties. The intrinsic luminosities of these AGNs are estimated to be -24 > MB > -26, but optical obscuration allows their host galaxies to be studied unencumbered by bright nuclei. Each object has been imaged in three continuum filters ('UV,' 'blue,' and 'yellow') placed between the strong emission lines. The spectacular, high-quality images reveal a wealth of details about the structure of the host galaxies and their environments. Six of the nine galaxies in the sample are elliptical galaxies with de Vaucouleurs light profiles, one object has a well-defined disk component, and the remaining two have marginal disks. Stellar populations of type II quasar hosts are more luminous (by a median of 0.3-0.7 mag, depending on the wavelength) and bluer (by about 0.4 mag) than are M* galaxies at the same redshift. When smooth fits to stellar light are subtracted from the images, we find both positive and negative residuals that become more prominent toward shorter wavelengths. We argue that the negative residuals are due to kiloparsec-scale dust obscuration, while most positive residuals are due to the light from the nucleus scattered off interstellar material in the host galaxy. Scattered light makes a significant contribution to the broadband continuum emission and can be the dominant component of the extended emission in the UV in extreme cases.
We present observations of the interstellar interloper 1I/2017 U1 ('Oumuamua) taken during its 2017 October flyby of Earth. The optical colors B - V = 0.70 0.06, V - R = 0.45 0.05, overlap those of ...the D-type Jovian Trojan asteroids and are incompatible with the ultrared objects that are abundant in the Kuiper Belt. With a mean absolute magnitude HV = 22.95 and assuming a geometric albedo pV = 0.1, we find an average radius of 55 m. No coma is apparent; we deduce a limit to the dust mass production rate of only ∼2 × 10−4 kg s−1, ruling out the existence of exposed ice covering more than a few m2 of the surface. Volatiles in this body, if they exist, must lie beneath an involatile surface mantle 0.5 m thick, perhaps a product of prolonged cosmic-ray processing in the interstellar medium. The light curve range is unusually large at ∼2.0 0.2 mag. Interpreted as a rotational light curve the body has axis ratio :1 and semi-axes ∼230 m × 35 m. A 6:1 axis ratio is extreme relative to most small solar system asteroids and suggests that albedo variations may additionally contribute to the variability. The light curve is consistent with a two-peaked period ∼8.26 hr, but the period is non-unique as a result of aliasing in the data. Except for its unusually elongated shape, 1I/2017 U1 is a physically unremarkable, sub-kilometer, slightly red, rotating object from another planetary system. The steady-state population of similar, ∼100 m scale interstellar objects inside the orbit of Neptune is ∼104, each with a residence time of ∼10 years.
Bright quasars at low z have generally been found in massive, evolved host galaxies, consistent with formation at early epochs. However, deep, high resolution, multicolor imaging of some quasar hosts ...have found morphological evidence of tidal tails and colors indicative of active star formation. These results are consistent with theories of galaxy formation and evolution in which merger processes trigger the activation of the quasar phase, and energetic feedback is essential. Understanding the role the black hole population plays in the galaxy formation process is important, but imaging the host galaxies around bright quasars is difficult because of the contribution of the bright nuclei. Very high resolution, deep imaging is necessary to successfully remove the nuclear component. We made high-resolution near-infrared images of several bright z ˜ 0.3 BL Lacs with the Gemini Multi-Conjugate Adaptive Optics System (GeMS)/GSAOI in order to study their host galaxies. We will present the results of this imaging with the 1 arcmin AO-corrected field provided by GeMS/GSAOI and compare with available HST imaging available in the archive.
Episodically Active Asteroid 6478 Gault Jewitt, David; Kim, Yoonyoung; Luu, Jane ...
Astrophysical journal. Letters,
05/2019, Letnik:
876, Številka:
2
Journal Article
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We present imaging and spectroscopic observations of 6478 Gault, a ∼6 km diameter inner main-belt asteroid currently exhibiting strong, comet-like characteristics. Three distinct tails indicate that ...ultra-slow dust (ejection speed 0.15 0.05 m s−1) was emitted from Gault in separate episodes beginning UT 2018 October 28 5 (Tail A), UT 2018 December 31 5 (Tail B), and UT 2019 February 10 7 (Tail C), with durations of ΔT ∼ 10-20 days. With a mean particle radius 200 m, the estimated masses of the tails are MA ∼ 4 × 107 kg, MB ∼ 6 × 106 kg, and MC ∼ 6 × 105 kg, respectively, and the mass-loss rates from the nucleus are 20-40 kg s−1 for Tail A, 4-6 kg s−1 for Tail B, and ∼0.4 kg s−1 for Tail C. In its optical colors Gault is more similar to C-type asteroids than to S-types, even though the latter are numerically dominant in the inner asteroid belt. A spectroscopic upper limit to the production of gas is set at 1 kg s−1. Discrete emission in three protracted episodes effectively rules out an impact origin for the observed activity. Sublimation driven activity is unlikely given the inner-belt orbit and the absence of detectable gas. In any case, sublimation would not easily account for the observed multiple ejections. The closest similarity is between Gault and active asteroid 311P/(2013 P5), an object showing repeated but aperiodic ejections of dust over a 9 month period. While Gault is 10 times larger than 311P/(2013 P5), and the relevant timescale for spin-up by radiation torques is ∼100 times longer, its properties are likewise most consistent with episodic emission from a body rotating near breakup.
We have made a spectroscopic survey of luminous AGNs and quasars selected in the mid-infrared from Spitzer IRAC surveys. Mid-infrared selection is less affected by dust obscuration, and we find more ...high redshift quasars than are found in optical or hard X-ray surveys. We have derived luminosity functions for obscured and unobscured quasar populations, and we use these and spectral energy distribution fits to place constraints on host galaxy properties and quasar lifetimes.
Active Asteroid P/2017 S5 (ATLAS) Jewitt, David; Kim, Yoonyoung; Rajagopal, Jayadev ...
The Astronomical journal,
02/2019, Letnik:
157, Številka:
2
Journal Article
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Observations of active asteroid P/2017 S5 when near perihelion reveal the ejection of large (102-104 m) particles at 0.2-2 m s−1 speeds, with estimated mass-loss rates of a few kg s−1. The protracted ...nature of the mass loss (continuous over ∼150 days) is compatible with a sublimation origin, meaning that this object is likely an ice-bearing main-belt comet. Equilibrium sublimation of exposed water ice covering as little as 0.1 km2 can match the data. Observations a year after perihelion show the object in an inactive state from which we deduce a nucleus effective radius (albedo 0.06 0.02 assumed). The gravitational escape speed from a body of this size is just ∼0.3 m s−1, comparable to the inferred ejection speed of the dust. Time-series photometry provides tentative evidence for rapid rotation (lightcurve period 1.4 hr) that may also play a role in the loss of mass and which, if real, is a likely consequence of spin-up by sublimation torques. P/2017 S5 shares both physical and orbital similarities with the split active asteroid pair P/2016 J1-A and J1-B, and all three objects are likely members of the ∼7 Myr old, collisionally produced, Theobalda family.
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