Abstract
We consider the energy budgets and radiative history of eight fading active galactic nuclei (AGNs), identified from an energy shortfall between the requirements to ionize very extended ...(radius > 10 kpc) ionized clouds and the luminosity of the nucleus as we view it directly. All show evidence of significant fading on timescales of ≈50,000 yr. We explore the use of minimum ionizing luminosity
Q
ion
derived from photoionization balance in the brightest pixels in H
α
at each projected radius. Tests using presumably constant Palomar–Green QSOs, and one of our targets with detailed photoionization modeling, suggest that we can derive useful histories of individual AGNs, with the caveat that the minimum ionizing luminosity is always an underestimate and subject to uncertainties about fine structure in the ionized material. These consistency tests suggest that the degree of underestimation from the upper envelope of reconstructed
Q
ion
values is roughly constant for a given object and therefore does not prevent such derivation. The AGNs in our sample show a range of behaviors, with rapid drops and standstills; the common feature is a rapid drop in the last ≈2 × 10
4
yr before the direct view of the nucleus. The
e
-folding timescales for ionizing luminosity are mostly in the thousands of years, with a few episodes as short as 400 yr. In the limit of largely obscured AGNs, we find additional evidence for fading from the shortfall between even the lower limits from recombination balance and the maximum luminosities derived from far-infrared fluxes. We compare these long-term light curves, and the occurrence of these fading objects among all optically identified AGNs, to simulations of AGN accretion; the strongest variations over these timespans are seen in models with strong and local (parsec-scale) feedback. We present Gemini integral-field optical spectroscopy, which shows a very limited role for outflows in these ionized structures. While rings and loops of emission, morphologically suggestive of outflow, are common, their kinematic structure shows some to be in regular rotation. UGC 7342 exhibits local signatures of outflows <300 km s
−1
, largely associated with very diffuse emission, and possibly entraining gas in one of the clouds seen in
Hubble Space Telescope
images. Only in the Teacup AGN do we see outflow signatures of the order of 1000 km s
−1
. In contrast to the extended emission regions around many radio-loud AGNs, the clouds around these fading AGNs consist largely of tidal debris being externally illuminated but not displaced by AGN outflows.
Abstract
The environment of the high-redshift (
z
= 1.408), powerful radio-loud galaxy 3C 297 has several distinctive features of a galaxy cluster. Among them, a characteristic halo of hot gas ...revealed by Chandra X-ray observations. In addition, a radio map obtained with the Very Large Array shows a bright hotspot in the northwestern direction, created by the interaction of the active galactic nucleus (AGN) jet arising from 3C 297 with its environment. In the X-ray images, emission cospatial with the northwestern radio lobe is detected, and peaks at the position of the radio hotspot. The extended, complex X-ray emission observed with our new Chandra data is largely unrelated to its radio structure. Despite having attributes of a galaxy cluster, no companion galaxies have been identified from 39 new spectra of neighboring targets of 3C 297 obtained with the Gemini Multi-Object Spectrograph. None of the 19 galaxies for which a redshift was determined lies at the same distance as 3C 297. The optical spectral analysis of the new Gemini spectrum of 3C 297 reveals an isolated Type II radio-loud AGN. We also detected line broadening in O
ii
λ
3728 with a FWHM about 1700 km s
−1
and possible line shifts of up to 500–600 km s
−1
. We postulate that the host galaxy of 3C 297 is a fossil group, in which most of the stellar mass has merged into a single object, leaving behind an X-ray halo.
NEBULAR is a lightweight code to synthesize the spectrum of an ideal, mixed hydrogen and helium gas in ionization equilibrium, over a useful range of densities, temperatures and wavelengths. ...Free-free, free-bound and two-photon continua are included as well as parts of the H i, He i and He ii line series. NEBULAR interpolates over publicly available data tables; it can be used to easily extract information from these tables without prior knowledge about their data structure. The resulting spectra can be used to e.g., determine equivalent line widths, constrain the contribution of the nebular continuum to a bandpass, and for educational purposes. NEBULAR can resample the spectrum on a user-defined wavelength grid for direct comparison with an observed spectrum; however, it can not be used to fit an observed spectrum.
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NEBULAR Schirmer, Mischa
Publications of the Astronomical Society of the Pacific,
11/2016, Volume:
128, Issue:
969
Journal Article
Peer reviewed
NEBULAR is a lightweight code to synthesize the spectrum of an ideal, mixed hydrogen and helium gas in ionization equilibrium, over a useful range of densities, temperatures and wavelengths. ...Free–free, free-bound and two-photon continua are included as well as parts of the H I, He I and He II line series. NEBULAR interpolates over publicly available data tables; it can be used to easily extract information from these tables without prior knowledge about their data structure. The resulting spectra can be used to e.g., determine equivalent line widths, constrain the contribution of the nebular continuum to a bandpass, and for educational purposes. NEBULAR can resample the spectrum on a user-defined wavelength grid for direct comparison with an observed spectrum; however, it can not be used to fit an observed spectrum.
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We demonstrate that deep good-seeing VLT/HAWK-I Ks images complemented with g + z-band photometry can yield a sensitivity for weak lensing studies of massive galaxy clusters at redshifts 0.7 ≲ z ≲ ...1.1, which is almost identical to the sensitivity of HST/ACS mosaics of single-orbit depth. Key reasons for this good performance are the excellent image quality frequently achievable for Ks imaging from the ground, a highly effective photometric selection of background galaxies, and a galaxy ellipticity dispersion that is noticeably lower than for optically observed high-redshift galaxy samples. Incorporating results from the 3D-HST and UltraVISTA surveys we also obtained a more accurate calibration of the source redshift distribution than previously achieved for similar optical weak lensing data sets. Here we studied the extremely massive galaxy cluster RCS2 J232727.7−020437 (z = 0.699), combining deep VLT/HAWK-I Ks images (point spread function with a 0.′′35 full width at half maximum) with LBT/LBC photometry. The resulting weak lensing mass reconstruction suggests that the cluster consists of a single overdensity, which is detected with a peak significance of 10.1σ. We constrained the cluster mass to $M_{\mathrm{200c}}/(10^{15}~{M}_{\odot}) =2.06^{+0.28}_{-0.26}(\mathrm{stat.})\pm 0.12 (\mathrm{sys.})$ M200c/(1015 M⊙) = 2.06−0.26+0.28(stat.) ± 0.12(sys.) M200c∕(1015M⊙)=2.06-0.26+0.28(stat.)±0.12(sys.) assuming a spherical Navarro, Frenk & White model and simulation-based priors on the concentration, making it one of the most massive galaxy clusters known in the z ≳ 0.7 Universe. We also cross-checked the HAWK-I measurements through an analysis of overlapping HST/ACS images, yielding fully consistent estimates of the lensing signal.
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We use deep Gemini/GMOS-S g, r photometry to study the three ultra-faint dwarf galaxy candidates DES1, Eridanus III (Eri III), and Tucana V (Tuc V). Their total luminosities, MV(DES1) = −1.42 0.50 ...and MV(Eri III) = −2.07 0.50, and mean metallicities, and , are consistent with them being ultra-faint dwarf galaxies, as they fall just outside the 1 confidence band of the luminosity-metallicity relation for Milky Way satellite galaxies. However, their positions in the size-luminosity relation suggest that they are star clusters. Interestingly, DES1 and Eri III are at relatively large Galactocentric distances, with DES1 located at and Eri III at . In projection, both objects are in the tail of gaseous filaments trailing the Magellanic Clouds and have similar 3D separations from the Small Magellanic Cloud (SMC): kpc and kpc, respectively. It is plausible that these stellar systems are metal-poor SMC satellites. Tuc V represents an interesting phenomenon in its own right. Our deep photometry at the nominal position of Tuc V reveals a low-level excess of stars at various locations across the GMOS field without a well-defined center. An SMC Northern Overdensity-like isochrone would be an adequate match to the Tuc V color-magnitude diagram, and the proximity to the SMC (12 1; kpc) suggests that Tuc V is either a chance grouping of stars related to the SMC halo or a star cluster in an advanced stage of dissolution.
Without the interference of a number of events, galaxies may suffer in crowded environments (e.g., stripping, harassment, strangulation); isolated elliptical galaxies provide a control sample for the ...study of galaxy formation. We present the study of a sample of isolated ellipticals using imaging from a variety of telescopes, focusing on their globular cluster systems as tracers of their stellar halos. Our main findings are: (a) GC color bimodality is common even in the most isolated systems; (b) the specific frequency of GCs is fairly constant with galaxy mass, without showing an increase towards high-mass systems like in the case of cluster ellipticals; (c) on the other hand, the red fraction of GCs follows the same inverted V shape trend with mass as seen in cluster ellipticals; and (d) the stellar halos show low Sérsic indices which are consistent with a major merger origin.
We obtained deep Gemini GMOS-S g, r photometry of the ultra-faint dwarf galaxy candidate Cetus II with the aim of providing stronger constraints on its size, luminosity, and stellar population. Cetus ...II is an important object in the size-luminosity plane, as it occupies the transition zone between dwarf galaxies and star clusters. All known objects smaller than Cetus II (rh ∼ 20 pc) are reported to be star clusters, while most larger objects are likely dwarf galaxies. We found a prominent excess of main-sequence stars in the color-magnitude diagram of Cetus II, best described by a single stellar population with an age of 11.2 Gyr, metallicity of Fe/H = −1.28 dex, an /Fe = 0.0 dex at a heliocentric distance of 26.3 1.2 kpc. As well as being spatially located within the Sagittarius dwarf tidal stream, these properties are well matched to the Sagittarius galaxy's Population B stars. Interestingly, like our recent findings on the ultra-faint dwarf galaxy candidate Tucana V, the stellar field in the direction of Cetus II shows no evidence of a concentrated overdensity despite tracing the main sequence for over six magnitudes. These results strongly support the picture that Cetus II is not an ultra-faint stellar system in the Milky Way halo, but made up of stars from the Sagittarius tidal stream.
Galaxy halos and their globular cluster systems build up over time by the accretion of small satellites. We can learn about this process in detail by observing systems with ongoing accretion events ...and comparing the data with simulations. Elliptical shell galaxies are systems that are thought to be due to ongoing or recent minor mergers. We present preliminary results of an investigation of the baryonic halo—light profile, globular clusters, and shells/streams—of the shell galaxy NGC 3923 from deep Dark Energy Camera (DECam) g and i-band imaging. We present the 2D and radial distributions of the globular cluster candidates out to a projected radius of about 185 kpc, or ∼ 37 R e , making this one of the most extended cluster systems studied. The total number of clusters implies a halo mass of M h ∼ 3 × 10 13 M ⊙ . Previous studies had identified between 22 and 42 shells, making NGC 3923 the system with the largest number of shells. We identify 23 strong shells and 11 that are uncertain. Future work will measure the halo mass and mass profile from the radial distributions of the shell, N-body models, and line-of-sight velocity distribution (LOSVD) measurements of the shells using the Multi Unit Spectroscopic Explorer (MUSE).
3C 17: The BCG of a Galaxy Cluster at z = 0.22 Madrid, Juan P.; Donzelli, Carlos J.; Rodríguez-Ardila, Alberto ...
The Astrophysical journal. Supplement series,
10/2018, Volume:
238, Issue:
2
Journal Article
Peer reviewed
Open access
Gemini Multi Object Spectrograph medium-resolution spectra and photometric data of 39 objects in the field of the radio galaxy 3C 17 are presented. Based on the new data, a previously uncataloged ...cluster of galaxies is identified at a mean redshift of z = 0.220 0.003, a projected virial radius of 0.37 Mpc, and a velocity dispersion of v = 821 171 km s−1. The brightest member of this cluster is 3C 17, with Mr = −22.45 mag. The surface brightness profile of 3C 17 is best fit with two components (Exponential + Sérsic) characteristic of brightest cluster galaxies. The spectrum of 3C 17 is dominated by broad emission lines H + N ii and Hβ + O iii. Analysis of Chandra data shows extended emission around the cluster core that supports the existence of hot gas cospatial with 3C 17. The discovery of a cluster of galaxies around 3C 17 better explains the sharply bent morphology of the radio jet given that it propagates through a dense intracluster medium.
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