Statistical Properties of Radio Galaxies in the local Universe

Yen-Ting LinPrinceton University

Pontificia Universidad Católica de ChileYue Shen, Michael Strauss, Ragnhild Lunnan (Princeton), Zheng

Zheng (IAS)

outline

• motivation• construction of the

sample• relationship with

radio-quiet (RQ) population

• dependence on the environment

• formation mechanism of radio galaxies (RGs)

credit: NRAO, J. Uson

NGC1316 + Fornax A

motivation: SZ surveys are happening!

credit: CXO

Carlstrom et al (2002)

Atacama Cosmology Telescope in construction

see Lin et al (0805.1750) for estimation of effects of radio sources on SZ signal

motivation: making the bright end of the

luminosity function right

• using NYU-VAGC DR6 LSS galaxy sample as parent sample, containing ~220,000 galaxies with measured redshifts down to Mr–20.5

• cross-matched with NVSS and FIRST surveys at 1.4 GHz to generate the largest radio galaxy catalog to date: 10,500 RGs

• studying luminosity function and clustering properties from volume-limited subsamples

the sample

correlation function

• both galaxies and RGs are volume-limited and subject to same optical luminosity cut (Mr–21.5)

• RGs (red) more strongly clustered than galaxies (blue)

• clustering length comparable to groups of galaxies (~10h-1Mpc)

correlation function: HOD modeling

• halo occupation distribution modeling suggests RGs are hosted by halos more massive than 1013 Msun

RGs in massive halos: halo occupation number

• count galaxies and RGs at Mr–20.5 in 134 X-ray clusters from ROSAT all-sky survey

• number of galaxies goes as M0.8

• occupation number of RGs not a strong function of cluster mass

• 1440 galaxies, 85 RGs (~6%)

• 61/134 (=45%) clusters host RGs

• among these, 34 have RL BCGs

• 42 clusters host only 1 RG, 19 of these are BCG

• 25% of BCGs are RL

• 4% of non-BCG galaxies are RL

• NOTE: only 1.9% of galaxies are RL globally

BCGs

clusters w/o RGs

RGs in massive halos: spatial distribution

RGs in dense regions

• excess number of neighbors– 1000 RGs, 1000 RQ

galaxies matched to optical luminosity, apparent magnitude, and redshift

– count nearby objects out to 2 Mpc from SDSS photometric catalog, within –23.5Mr–20.5

– within ~0.5 Mpc, RL galaxies always have higher number of neighbors than RQ ones

Mpc

RGs in dense regions

no RLAGN–SF galaxy pairs atscales<1Mpc!

conclusion

• observations:– given optical luminosity and color, RGs are more strongly clustered

than the corresponding RQ galaxy sample

– large scale clustering implies hosts are group or cluster-sized halos

– RGs very centrally concentrated towards halo center

• ingredients for RL AGN phenomenon– dense environment

– presence of intracluster/intragroup gas: confining pressure?

– low level supply of gas: mass loss from old stars?

• further tests– halo occupation number in optical-selected clusters

– environment of high and low-excitation RL AGNs (e.g., FRI vs FRII)

– matching with X-ray AGNs