Why z &gt; 1 radio-loud galaxies are commonly located in protoclusters

et al. 2016

ApJ

Using Hubble Space Telescope slitless grism data, we report the spectroscopic confirmation of two distant structures atz 2 associated with powerful high-redshift radio-loud active galactic nuclei(AGNs). These rich structures, likely (forming) clusters, are among the most distant structures currently known, and were identified on the basis of Spitzer/IRAC [3.6]-[4.5] color. We spectroscopically confirm nine members in the field of MRC2036 −254, comprising eight star-forming galaxies and the targeted radio galaxy. The median redshift is z=2.000. We spectroscopically confirm 10 members in the field of B30756+406, comprising 8 star-forming galaxies and 2 AGNs, including the targeted radio-loud quasar. The median redshift is z=1.986. All confirmed members are within 500 kpc (1 arcmin) of the targeted AGNs. We derive median (mean) star-formation rates of based on mid-infrared fluxes and spectral energy distribution modeling. Most of our confirmed members are located above the star-forming mainsequence toward starburst galaxies, consistent with clusters at these early epochs being the sites of significant levels of star formation. The structure around MRC2036−254 shows an overdensity of IRAC-selected candidate galaxy cluster members consistent with being quiescent galaxies, while the structure around B30756+406 shows field values, albeit with many lower limits to colors that could allow an overdensity of faint red quiescent galaxies. The structure around MRC2036−254 shows a red sequence of passive galaxy candidates.

Section: Introductionsupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

HST GRISM CONFIRMATION OF TWO z ∼ 2 STRUCTURES FROM THE CLUSTERS AROUND RADIO-LOUD AGN (CARLA) SURVEY

Noirot

Vernet

et al. 2016

ApJ

“…Unfortunately, the observing program committee of ESO only granted us narrowband imaging of TXS 2353-003, not of NVSS J210626-314003, so that we were unable to do a narrowband search around this galaxy. We note, however, that selecting a galaxy based on its bright radio emission already leads to significant biases toward galaxies in dense environments (e.g., Best 2000;Ramos Almeida et al 2013;Hatch et al 2014), and we argue in the following that the stellar component of NVSS J210626-314003 itself shows some of the characteristic signatures of cluster central galaxies. Kauffmann & Charlot (1998) argued that the observed K-band magnitude can be used to approximate the stellar mass of all but the most rapidly growing galaxies out to redshifts z ≥ 2, with a scatter of about a factor of 2.…”

Section: Comparison Of Txs 2353-003 and Nvss J210620-214003 With Clusmentioning

confidence: 66%

Defying jet-gas alignment in two radio galaxies atz~ 2 with extended light profiles: Similarities to brightest cluster galaxies

Collet

Nesvadba

et al. 2015

A&A

Self Cite

We report the detection of extended warm ionized gas in two powerful high-redshift radio galaxies, NVSS J210626-314003 at z = 2.10 and TXS 2353-003 at z = 1.49, that does not appear to be associated with the radio jets. This is contrary to what would be expected from the alignment effect, a characteristic feature of distant, powerful radio galaxies at z ≥ 0.6. The gas also has smaller velocity gradients and line widths than most other high-z radio galaxies with similar data. Both galaxies are part of a systematic study of 50 high-redshift radio galaxies with SINFONI, and are the only two that are characterized by the presence of high surface-brightness gas not associated with the jet axis and by the absence of such gas aligned with the jet. Both galaxies are spatially resolved with ISAAC broadband imaging covering the rest-frame R band, and have extended wings that cannot be attributed to line contamination. We argue that the gas and stellar properties of these galaxies are more akin to gas-rich brightest cluster galaxies in cool-core clusters than the general population of high-redshift radio galaxies at z > ∼ 2. In support of this interpretation, one of our sources, TXS 2353-003, for which we have Hα narrowband imaging, is associated with an overdensity of candidate Hα emitters by a factor of ∼8 relative to the field at z = 1.5. We discuss possible scenarios of the evolutionary state of these galaxies and the nature of their emission line gas within the context of cyclical AGN feedback.

“…It thus appears possible that the majority of massive galaxies experienced such a phase of moderate radio activity if these phases were sufficiently short (a few 10 7 yrs, see also Venemans et al 2007;Nesvadba et al 2008b). By studying a sample of radio-selected galaxies, we might expect to predominantly probe galaxies in dense environments (Best 2000;Hatch et al 2014). Eight of our sources are part of the CARLA survey (Wylezalek et al 2013) with Spitzer, which measures the density of galaxies with mid-infrared colors consistent with being at redshifts z ≥ 1.3 around HzRGs.…”

Section: A Generic Phase In the Evolution Of Massive High-redshift Gamentioning

confidence: 99%

Kinematic signatures of AGN feedback in moderately powerful radio galaxies atz~ 2 observed with SINFONI

Collet

Nesvadba

et al. 2016

A&A

Self Cite

Most successful galaxy formation scenarios now postulate that the intense star formation in massive, high-redshift galaxies during their major growth period was truncated when powerful AGNs launched galaxy-wide outflows of gas that removed large parts of the interstellar medium. SINFONI imaging spectroscopy of the most powerful radio galaxies at z ∼ 2 show clear signatures of such winds, but are too rare to be good representatives of a generic phase in the evolution of all massive galaxies at high redshift. Here we present SINFONI imaging spectroscopy of the rest-frame optical emission-line gas in 12 radio galaxies at redshifts ∼2. Our sample spans a range in radio power that is intermediate between the most powerful radio galaxies with known wind signatures at these redshifts and vigorous starburst galaxies, and are about two orders of magnitude more common than the most powerful radio galaxies. Thus, if AGN feedback is a generic phase of massive galaxy evolution for reasonable values of the AGN duty cycle, these are just the sources where AGN feedback should be most important. Our sources show a diverse set of gas kinematics ranging from regular velocity gradients with amplitudes of Δv = 200−400 km s −1 consistent with rotating disks to very irregular kinematics with multiple velocity jumps of a few 100 km s −1 . Line widths are generally high, typically around FWHM = 800 km s −1 , more similar to the more powerful high-z radio galaxies than mass-selected samples of massive high-z galaxies without bright AGNs, and consistent with the velocity range expected from recent hydrodynamic models. A broad Hα line in one target implies a black hole mass of a few 10 9 M . Velocity offsets of putative satellite galaxies near a few targets suggest dynamical masses of a few 10 11 M for our sources, akin to the most powerful high-z radio galaxies. Ionized gas masses are 1−2 orders of magnitude lower than in the most powerful radio galaxies, and the extinction in the gas is relatively low, up to A V ∼ 2 mag. The ratio of line widths, σ, to bulk velocity, v, is so large that even the gas in galaxies with regular velocity fields is unlikely to be gravitationally bound. It is unclear, however, whether the large line widths are due to turbulence or unresolved, local outflows as are sometimes observed at low redshifts. We compare our sources with sets of radio galaxies at low and high redshift, finding that they may have more in common with gas-rich nearby radio galaxies with similar jet power than with the most powerful high-z radio galaxies. Comparison of the kinetic energy with the energy supply from the AGNs through jet and radiation pressure suggests that the radio source still plays a dominant role for feedback, consistent with low-redshift radio-loud quasars.