Lecture 11: SDSS Sources at Other Wavelengths: From X rays to radio. Astr 598: Astronomy with SDSS

Transcription

1 Astr 598: Astronomy with SDSS Spring Quarter 4, University of Washington, Željko Ivezić Lecture : SDSS Sources at Other Wavelengths: From X rays to radio

2 Large Surveys at Many Wavelengths SDSS: UV-IR five-band photometry for million galaxies and million quasar candidates, spectra for million galaxies and, quasars MASS: near-ir (JHK) for.65 million resolved sources, and 47 million point sources GALEX: far-uv ( bands:. and. µm), all-sky survey to m AB.5, 4 deg to m AB 6, spectroscopy for, galaxies, angular resolution 4-6 arcsec ROSAT, Chandra, XMM: X-rays (soft and hard), energetic processes, hard X-rays penetrate dust (important for AGNs) IRAS, ISO, Spitzer: dust emission, high-redshift sources FIRST, NVSS, WENSS, GB6: Radio surveys, good for AGNs

3 SDSS Sources Which of these SDSS sources are detected by surveys at other wavelengths? unresolved optically resolved

4 Champ - SDSS DR sources (yellow:unresolved, green:resolved) unresolved 4 optically resolved SDSS-Chandra Sources Wavelength: soft/hard X rays (.5-8 kev), Depth: m AB < 4, Astrometric accuracy arcsec A small fraction of SDSS sources are detected by Chandra; mostly fainter than SDSS spectroscopic limits Point sources dominated by quasars; also some active (M) stars Galaxies dominated by AGN hosts Potential: X-ray part of SED; AGN population census (especially for obscured sources), stellar activity 4

5 unresolved optically resolved SDSS-GALEX Sources Wavelength: UV, Depth: m AB <.5, Astrometric accuracy arcsec A small fraction of SDSS sources are detected by GALEX; a good fraction of stars have spectra, galaxies mostly fainter than SDSS spectroscopic limit Point sources dominated by hot blue (turn-off) stars; also some quasars Galaxies dominated by blue starburst galaxies Potential: UV part of SED, estimates of star-formation rate and its dependence on other parameters, dust 5

6 SDSS-MASS sources Red: unresolved by SDSS, blue: resolved by SDSS, magenta: resolved by MASS Bright stars (blue with r<8, red with r<) detected by MASS (fluxlimited in K band) SDSS main spectroscopic galaxy sample detected by MASS, about 3% resolved by MASS J K = is a good stargalaxy separator 6

7 SDSS-MASS sources Blue/red: blue and red stars; green/magenta: blue and red galaxies, Circles: quasars (z <.5) Optical/IR colors allow an efficient star-quasar-galaxy separation 8-band accurate and robust photometry excellent for finding objects with atypical SEDs (e.g. red AGNs, L/T dwarfs, binary stars) 7

8 4 SDSS DR spectroscopic sample of galaxies -4 SDSS main galaxies Bimodal color distribution Red galaxies more numerous than blue galaxies Red galaxies at larger redshifts/larger luminosities How do such distributions appear for galaxies detected by other surveys?

9 MASS XSC galaxies (dots) in SDSS DR (contours) SDSS-MASS XSC main galaxies MASS XSC is complete for galaxies with r P et < 6.3 MASS XSC is biased towards red galaxies SDSS and MASS filters

10 SDSS-MASS XSC galaxies ( ) SDSS-MASS: galaxy SEDs The fact that galaxy SEDs are nearly one-parameter family at SDSS wavelengths extends to MASS wavelengths Using SDSS u and r band fluxes, it is possible to predict MASS K band flux to within. mag! (astrophysical scatter only. mag) common wisdom : such a relationship should not be so accurate due to the effects of starbursts and dust extinction SDSS MASS

11 SDSS-IRAS main galaxies IRAS is never complete, the fraction of IRAS-detected galaxies decreases fast with r P et IRAS is biased towards blue galaxies (dusty galaxies: AGNs and star-forming) As a result of color-luminosity relation, IRAS-detected galaxies biased towards lower redshifts

12 3 AGN and SFs in MASS and IRAS with K<4.3 and.<z<.5.5 SDSS-MASS-IRAS galaxies: AGNs vs. star-forming Optical-IR colors for AGNs vs. star-forming galaxies (separated using BPT diagram) AGN galaxies have redder z K and J K colors (. and. mag, respectively), and bluer z m 6 color ( mag) than starforming galaxies. The redder z m 6 color observed for star-forming galaxies than for AGN galaxies is due to more UV light reprocessed by the (smaller amount of) dust

13 SDSS-FIRST main galaxies Radio galaxies are biased towards red luminous galaxies Bias towards red galaxies is a result of K correction: when compared in narrow redshift bins, there is no color difference All SDSS-FIRST galaxies (red dots) compared to all SDSS galaxies (blue contours) 3

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15 Adding radio information to the BPT diagram Symbols in the BPT diagram (upper left) are colorcoded by the position in the M rp et vs. α 9 diagram (lower left) Only luminous galaxies (M rp et < ) have flat radio spectra, and are found in the AGN region of the BPT diagram Galaxies in the star-forming region of the BPT diagram have steep radio spectra, and are not very luminous (M rp et > ) 5

16 Radio galaxies without emission lines Cannot place them in the BPT diagram Radio subsample biased towards larger redshift (observed u r colors are redder due to K-correction) More luminous by mag than radio galaxies with emission lines A few that are bluish have very small luminosities (and smaller concentration parameter) Have steep radio spectra 6

17 FIRST sources with SDSS detections About % of SDSS- FIRST sources (with r < ) are optically unresolved The fraction of optically unresolved SDSS-FIRST sources decreases with radio flux SDSS quasars with FIRST detections are slightly (. mag) redder than other quasars 7

18 < i < < i < < i < 9 Is there radio bimodality for quasars? Is the distribution of radioto-optical flux ratio bimodal (i.e. does it have a local minimum)? Yes, but need to be careful about selection effects. Must K-correct on an object-by-object basis. What is radio bimodality telling us?