We describe our efforts to understand large-scale (10's-100's kpc)
relativistic jet systems through observations of the highest-redshift quasars.
Results from a VLA survey search for radio jets in ~30 z>3.4 quasars are
described along with new Chandra observations of 4 selected targets.Comment: 5 pages, 2 figures, to appear in Extragalactic Jets: Theory and
  Observation from Radio to Gamma Ray, Eds. T.A. Rector and D.S. De Youn

Cheung, C. C.

Gobeille, D.

Harris, D. E

Lee, N. P.

Schwartz, D. A.

Siemiginowska, A.

Stawarz, L.

Wardle, J. F. C.

English

arXiv

Stawarz, Łukasz

Harris, D. E.

Jagiellonian Univeristy Repository

The highest redshift relativistic jets

We describe our efforts to understand large-scale (10's-100's kpc) relativistic jet systems through observations of the highest-redshift quasars. Results from a VLA survey search for radio jets in {approx} 30 z &gt; 3.4 quasars are described along with new Chandra observations of 4 selected targets

Cheung, C.C.

Harris, D.E

Schwartz, D.A.

Wardle, J.F.C.

Lee, N.P.

UNT Digital Library

Work supported in part by US Department of Energy contract DE-AC02-76SF00515The Highest Redshift Relativistic JetsC. C. Cheung1,  L. StawarzKavli Institute for Particle Astrophysics and Cosmology,Stanford University, Stanford, CA 94305A. Siemiginowska, D. E Harris, D. A. SchwartzHarvard-Smithsonian Center for Astrophysics,60 Garden St., Cambridge, MA 02138J. F. C. Wardle, D. GobeillePhysics Department, Brandeis University, Waltham, MA 02454N. P. LeeInstitute for Astrophysical Research, Boston University,725 Commonwealth Ave., Boston, MA 02215Abstract. We describe our eﬀorts to understand large-scale (10’s–100’s kpc)relativistic jet systems through observations of the highest-redshift quasars. Re-sults from a VLA survey search for radio jets in ∼30 z>3.4 quasars are describedalong with new Chandra observations of 4 selected targets.1. Why High-redshift Jets?It is now well established that X-ray emission is a common feature of kiloparsec-scale radio jets (see Harris & Krawczynski 2006, for a recent review and theassociated website, http://hea-www.harvard.edu/XJET/). The spectral energydistributions (SEDs) of the powerful quasar jets are predominantly characterizedas “optically faint”, with the spectra rising between the optical and X-ray bands.Current models for this ‘excess’ X-ray emission posit either inverse Compton (IC)scattering oﬀ CMB photons in a (still) relativistic kpc-scale jet or an additionalhigh-energy synchrotron emitting component.In the simplest scenario, such models have diverging predictions at high red-shift. Speciﬁcally, we expect a strong redshift dependence in the monochromaticﬂux ratio, fX/fr ∝ UCMB ∝ (1 + z)4 for IC/CMB, whereas in synchrotronmodels, we expect no such dependence, fX/fr ∝ (1 + z)0. As a ﬁrst ordertest of this simple idea, our approach is to study the highest-redshift relativisticjets. Such jets probe the physics of the earliest (ﬁrst ∼1 Gyr of the Universein the quasars studied) actively accreting supermassive black hole systems and1Jansky Postdoctoral Fellow of the National Radio Astronomy ObservatorySLAC-PUB-13055arXiv:0712.1192v1[astro-ph]December 2007Contributed to International Meeting On Extragalactic Jets: Theory And Observation From Radio To Gamma Ray ,21-24 May 2007, Girdwood, Alaska2 Cheung et al.are interesting for other reasons. For instance, the ambient medium in thesehigh-redshift galaxies is probably diﬀerent (e.g., De Young 2006) and this maymanifest in jets with diﬀerent morphologies, increased dissipation, and slowerthan their lower-redshift counterparts.DECLINATION (J2000)RIGHT ASCENSION (J2000)06 24 19.2 19.1 19.0 18.9 18.838 56 515049484746DECLINATION (J2000)RIGHT ASCENSION (J2000)20 42 57.50 57.45 57.40 57.35 57.30 57.25 57.20 57.15 57.10 57.05-22 23 242526272829DECLINATION (J2000)RIGHT ASCENSION (J2000)22 19 35.55 35.50 35.45 35.40 35.35 35.30 35.25 35.20 35.15 35.10-27 19 01020304050607DECLINATION (J2000)RIGHT ASCENSION (J2000)22 20 27.20 27.15 27.10 27.05 27.00 26.95 26.90 26.85 26.80 26.75-33 36 57585937 00010203Figure 1. Examples of newly discovered arcsecond-scale radio jets fromour VLA observations (§ 2.1.). Clockwise from upper left, the sources areJ0624+3856 (z=3.469; Xu et al. 1995), J2042–2223 (z=3.630; Hook et al.2002), J2220–3336 (z=3.691; Hook et al. 2002), and J2219–2719 (z=3.634;Hook et al. 2002). The J2219–2719 image is at 1.4 GHz while the rest areat 5 GHz. The beam-sizes are 0.41′′ × 0.41′′, 0.73′′ × 0.38′′ at PA=−8.2◦,1.13′′ × 0.39′′ at PA=10.2◦, and 0.75′′ × 0.75′′ (super-resolved), respectively.The lowest contour levels begin at 0.125 mJy/bm for all images except forJ2219–2719 where it is 0.2 mJy/bm, and increase by factors of√2.Most Chandra studies of quasar jets have so far targeted known arcsecond-scale radio jets (e.g., Sambruna et al. 2004; Marshall et al. 2005), as most knownexamples are at z <∼2 (Liu & Zhang 2002). There are currently only two high-zquasars with well-established kpc-scale X-ray jet detections: GB 1508+5714 atz=4.3 (Siemiginowska et al. 2003; Yuan et al. 2003; Cheung 2004) and 1745+624at z=3.9 (Cheung et al. 2006). They are observed to have large fX/fr valuesas expected in the IC/CMB model (Schwartz 2002; Cheung 2004), although theHighest-redshift Jets 3small number of high-z detections preclude any deﬁnitive statements (Kataoka & Stawarz2005; Cheung et al. 2006).We have therefore carried out a VLA survey in search of new radio jets ina sample of high-z quasars (§ 2.1.) and new Chandra observations of a smallsubset (§ 2.2.). This contribution presents some results from these observations.For the redshifts considered, z=3.4 to 4.7, 1′′ corresponds to 7.4 to 6.5 kpc(H0 = 70 km s−1 Mpc−1, ΩM = 0.3 and ΩΛ = 0.7).2. Observations of a High-Redshift Quasar Sample2.1. VLA Imaging SurveyUsing NED, we assembled a sample of z>3.4 ﬂat-spectrum radio quasars forimaging with the VLA. We did not aim for our sample to be a complete oneas current samples of lower-z X-ray jets are inhomogenous also. With archival(Lee 2005) and new VLA observations, we ﬁnd that radio jets in this redshiftrange are common with a ∼50% detection rate (Cheung et al. 2005, and inpreparation). Examples of new radio jets detected from our observations areshown in Figure 1.2.2. Chandra ObservationsA small percentage of the radio jets from our radio study (§ 2.1.) are extendedenough (>2.5” long) to study with Chandra. We observed four of them withshort snapshot Chandra observations (Figure 2). We detected bright X-raycounterparts to the jets in the quasars J1421–0643 (z=3.689; Ellison et al. 2001)and GB 1428+4217 (z=4.72; Hook & McMahon 1998); the latter detection iscurrently the highest-redshift kpc-scale radio and X-ray jet known. We didnot detect the X-ray counterparts to the radio jets in 1239+376 (z=3.819;Vermeulen et al. 1996) and J1754+6737 (z=3.6; Villani & di Serego Alighieri1999). The 2/4 X-ray jet detection rate of our high-z sample is comparableto that of lower-z samples (Sambruna et al. 2004; Marshall et al. 2005).3. Discussion and SummaryPrevious Chandra imaging studies of a number of z>4 radio loud quasars donot reveal signiﬁcant extended X-ray emission (Bassett et al. 2004; Lopez et al.2006). However, in these studies, there were no pre-existing information onpossible radio structures in the target objects and any deﬁnitive statementsregarding the nature of the X-ray emission mechanism in jets at high-redshiftsmay be premature. In fact, in one case where there was evidence of an extendedX-ray structure (J2219–2719; Lopez et al. 2006), our VLA observation revealeda radio counterpart (Figure 1).In our approach, we began with a VLA survey of a sample of z>3.4 quasarsand found radio jets to be relatively common (∼50% detection rate). These jetsare quite luminous; with a conﬁdent detection of a 1 mJy knot at 1.4 GHz, thiscorresponds to luminosities of 1.5 ×1042 erg s−1 (z=3.4) to 3.1 ×1042 erg s−1(z=4.7).4 Cheung et al.5 arcsecJ1754+6737 (z=3.6)5 arcsecGB 1428+4217 (z=4.7)5 arcsecJ1421-0643 (z=3.7)5 arcsec1239+376 (z=3.8)Figure 2. Chandra X-ray images (colorscale) with VLA contours overlaidof the four high-z radio jets observed. There are X-ray detections of the toptwo objects but not of the bottom two (§ 2.2.).With the radio survey results, we found only a few radio jets to have suﬃ-cient angular extent to be imaged with Chandra. The detection rate of X-raycounterparts of the high-z radio jets (2/4) is similar to that of lower-z radio jetsamples (Sambruna et al. 2004; Marshall et al. 2005). The implications of theseobservations for models of X-ray emission from large-scale jets will be describedin forthcoming publications.Acknowledgments. The National Radio Astronomy Observatory is op-erated by Associated Universities, Inc. under a cooperative agreement withthe National Science Foundation. This research was funded in part by NASAthrough contract NAS8-39073 (A. S., D. E. H., D. A. S.) and Chandra AwardNumbers GO7-8114 (C. C. C.,  L. S., J. F. C. W., D .G.) issued by the ChandraX-Ray Observatory Center, which is operated by the Smithsonian AstrophysicalObservatory for and on behalf of NASA under contract NAS8-39073. Radioastronomy at Brandeis University is supported by the NSF and NASA.  L. S. issupported by MEiN through research project 1-P03D-003-29 from 2005-2008.Highest-redshift Jets 5ReferencesBassett, L. C., et al. 2004, AJ, 128, 523Cheung, C.C. 2004, ApJ, 600, L23Cheung, C.C., Wardle, J.F.C., & Lee, N.P. 2005, in 22nd Texas Symposium on Rela-tivistic Astrophysics, Eds. P. Chen et al., (Palo Alto: SLAC) 1613Cheung, C.C., Stawarz,  L., & Siemiginowska, A. 2006, ApJ, 650, 679De Young, D. 2006, Astron. Nachr., 327, 231Ellison, S. L., Yan, L., Hook, I. M., Pettini, M., Wall, J. V., & Shaver, P. 2001, A&A,379, 393Harris, D.E., Krawczynski, H. 2006, ARAA, 44, 463Hook, I.M., & McMahon, R.G. 1998, MNRAS, 294, L7Hook, I.M., McMahon, R.G., Shaver, P.A., & Snellen, I.A.G. 2002, A&A, 391, 509Kataoka, J., & Stawarz,  L. 2005, ApJ, 622, 797Lee, N. P. 2005, Undergraduate Honors Thesis, Brandeis UniversityLiu, F. K., & Zhang, Y. H. 2002, A&A, 381, 757Lopez, L. A., Brandt, W. N., Vignali, C., Schneider, D. P., Chartas, G., & Garmire,G. P. 2006, AJ, 131, 1914Marshall, H. L., et al. 2005, ApJS, 156, 13Sambruna, R. M., Gambill, J. K., Maraschi, L., Tavecchio, F., Cerutti, R., Cheung,C. C., Urry, C. M., & Chartas, G. 2004, ApJ, 608, 698Schwartz, D.A. 2002, ApJ, 569, L23Siemiginowska, A., Smith, R.K., Aldcroft, T.L., Schwartz, D.A., Paerels, F., & Petric,A.O. 2003, ApJL, 598, L15Vermeulen, R. C., Taylor, G. B., Readhead, A. C. S., & Browne, I. W. 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The Highest Redshift Relativistic Jets

The Highest Redshift Relativistic Jets

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