Cold gas at high redshifts. R. Srianand Inter-University Center for Astronomy & Astrophysics, Pune - India

Transcription

1 Cold gas at high redshifts R. Srianand Inter-University Center for Astronomy & Astrophysics, Pune - India

2 Why cold gas? Stars are formed from the cold gas. IAS, Bangalore,Nov,

3 Why cold gas? Physical conditions (temperature, density and radiation field etc) of the gas are influenced by the local radiation field, the cosmic ray energy density, photoelectric heating by dust as well as mechanical energy input from both impulsive disturbances such as supernova explosions as well as more steady injection of energy in the form of stellar winds. All the sources of energy injection are related to in situ starformation Therefore, understanding physical conditions and the processes that maintain these are important for our understanding of galaxies and their evolution. IAS, Bangalore,Nov,

4 Why 21-cm absorbers? To measure the physical conditions in the neutral gas Measuring the spin temperature (multiphase ISM at high-z) Correlation between spin-temperature and metallicity/dust/starformation rate Probing the turbulence Measuring the magnetic field through Zeeman splitting Variations of fundamental constants IAS, Bangalore,Nov,

5 Detecting H I through 21 cm line: H I for an optically thin cloud that covers a fraction f c of the background source is related to the optical depth τ(v) in a velocity interval v and v+dv and to the spin temperature (T s ) by N(H I) = T s f c τ(v) dv cm 2. (1) If we assume the absorption line to have a perfect Gaussian profile with a peak optical depth τ P, then the above equation will become, N(H I) = τ P T S V cm 2 (2) where V = 2 ln 2 b is the FWHM of the Gaussian profile with b the Doppler parameter. IAS, Bangalore,Nov,

6 High-z 21-cm absorbers: Using data from Curran et al. 2005, Kanekar et al. 2006,2007 Typeset by FoilTEX IAS, Bangalore,Nov,

7 QSO SPECTRUM: Absorption lines Typeset by FoilTEX IAS, Bangalore,Nov,

8 QSOABS: H I absorption log N(H I) 17 Ly α forest. log N(H I) 20 DLA log N(H I) 17 LLS Typeset by FoilTEX IAS, Bangalore,Nov,

9 Our ongoing surveys: GMRT mini-survey of QSO-Gal pairs: z 0.3 GMRT 610 MHz survey: 1.1 z 1.45 GMRT/GBT/Arecibo/WSRT Survey: 0.7 z 1.45 GMRT/GBT DLA survey: 2 z 3.4 Typeset by FoilTEX IAS, Bangalore,Nov,

10 QSO absorber-galaxy Pairs: 2 Gupta et al DECLINATION (J2000) DECLINATION (J2000) RIGHT ASCENSION (J2000) RIGHT ASCENSION (J2000) DECLINATION (J2000) DECLINATION (J2000) RIGHT ASCENSION (J2000) RIGHT ASCENSION (J2000) DECLINATION (J2000) RIGHT ASCENSION (J2000) Team: Neeraj Gupta (PI), Srianand, David Bowen, York, Roy and Wadadekar c 2009 RAS, MNRAS 000, 1?? Typeset by FoilTEX IAS, Bangalore,Nov,

11 QSO absorber-galaxy Pairs: Typeset by FoilTEX IAS, Bangalore,Nov,

12 QSO absorber-galaxy Pairs: Typeset by FoilTEX IAS, Bangalore,Nov,

13 SDSS-GMRT sample of Mg II systems: Detection of Mg II systems in SDSS-DR7 with W(Mg II) 1Å using an automatic procedure. Select the systems with 1.15 z 1.45 (2893 systems) Cross-correlate the SDSS QSO with NVSS and FIRST. Pick the systems with flux density at the redshifted 21 cm wavelength greater than 50 mjy (37 systems). 400hrs of observations are completed-and we now have 9 new detections. Five systems are in front of radio sources that are compact at milli-arcsec scales. TEAM: R. Srianand (PI), Neeraj Gupta (ATNF), D.J. Saikia(NCRA), P. Petitjean(IAP), P. Notredome (IUCAA) Typeset by FoilTEX IAS, Bangalore,Nov,

14 Automatic selection of Mg II systems: Typeset by FoilTEX IAS, Bangalore,Nov,

15 GMRT sample of 21-cm absorption: Typeset by FoilTEX IAS, Bangalore,Nov,

16 2170Å dust feature towards J Typeset by FoilTEX IAS, Bangalore,Nov,

17 2170Å dust feature towards J Typeset by FoilTEX IAS, Bangalore,Nov,

18 GMRT spectra: Typeset by FoilTEX IAS, Bangalore,Nov,

19 Redshift evolution of 21cm absorbers: Typeset by FoilTEX IAS, Bangalore,Nov,

20 Figure 1: Left: Redshift distribution of the optimally selected Mg ii systems (shaded histogram in blue) and the DLAs (shaded histogram in magenta) proposed for the VLBA observations here. Distribution of the Mg ii systems in front of the compact radio sources imaged as part of the proposal VLBA/08C-101 is shown as the line histogram in red. Right: The ratio of W r (Mg iλ2852)/w r (Mg iiλ2796) versus the covering factor, f c. The filled and open circles are Redshift evolution of 21cm absorbers: for systems with and without 21cm absorption, respectively Figure 2: VLBA 20cm images of some of the sources observed as part of the project: VLBA/08C The typical rms is 0.15 mjy and the flux density ranges from 30 mjy to 700 mjy. sources typically for 30mins using nodding style phase referencing. We will observe sources in a cycle of 4mins, 3mins on source and 1min on phase referencing calibrator. 30mins on-source time will be split into three 10mins scans at different hour angles to improve the UV-coverage. This will allow us to achieve an rms of 0.2 mjy per polarization for very source. Rms per baseline per Typeset by FoilTEX IAS, Bangalore,Nov,

21 Optical absorption vs 21-cm detection Typeset by FoilTEX IAS, Bangalore,Nov,

22 SDSS-GMRT-Arecibo-WSRT-GBT:Optimal Based on the GMRT survey we have come up with optimal selection criteria that enable high detection rate of 21-cm absorption. 15 systems are found between 0.7 z Observations of 4 systems with GMRT is completed in June 09. We have 3 new detection. 10 systems are just now been observed at Arecibo. TEAM: R. Srianand (PI), Neeraj Gupta (ATNF), P. Petitjean(IAP), P. Notredome (IUCAA) Typeset by FoilTEX IAS, Bangalore,Nov,

23 GMRT preliminary results Typeset by FoilTEX IAS, Bangalore,Nov,

24 SDSS-GMRT-GBT sample of DLAs: Detection of DLAs at 2.2 z 3.5 in SDSS-DR7 with using an automatic procedure (Noterdaeme et al. 2009, A&A in press). Cross-correlate the SDSS QSO with NVSS and FIRST. Rejected systems that fall in the known RFI affected frequencies. Pick the systems with flux density at the redshifted 21 cm wavelength greater than 100 mjy (12 systems). All sources were imaged at GMRT in 610 MHz and 320 MHz. GMRT observations of 5 systems has resulted in one detection. GBT data are being analysed. We will propose for the VLBI in the next cycle. TEAM: R. Srianand (PI), Neeraj Gupta (ATNF), P. Petitjean(IAP), P. Notredome (IUCAA) Typeset by FoilTEX IAS, Bangalore,Nov,

25 Preliminary analysis: at z = 3.17 Heliocentric frequency (MHz) Typeset by FoilTEX IAS, Bangalore,Nov,

26 Preliminary analysis: at z = 3.17 Typeset by FoilTEX IAS, Bangalore,Nov,

27 Preliminary analysis: at z = 3.17 Typeset by FoilTEX IAS, Bangalore,Nov,

28 Preliminary analysis: at z = 3.17 Typeset by FoilTEX IAS, Bangalore,Nov,

29 Using 21-cm absorption lines: x = α 2 G p /µ x x = (x z x 0 ) x 0 = z UV z 21 1+z 21 Tubes & Wolfe (1980). The most recent measurements are from Tzanavaris et al. (2007). x/x = (0.63 ± 0.99) 10 5 over 0.23 z 2.35 using a heterogeneous sample of 21-cm absorption systems. ISSUES Associating of 21cm and UV absorption. Radio morphology. Typeset by FoilTEX IAS, Bangalore,Nov,

30 constraining constants: System 1 PLot file version 1 created 31-JUL :39:22 CONT: J IPOL MHZ J ICL Center at RA DEC Cont peak flux = E-02 JY/BEAM Levs = 2.000E-03 * (-1, 1, 2, 4, 8, 16, 32, 64, 128, 256, 512) 8.3 MHz 2.3 MHz 1.4 MHz Typeset by FoilTEX IAS, Bangalore,Nov,

31 Preliminary analysis: System 1 x/x = 0.0 ± at z = 1.36 Typeset by FoilTEX IAS, Bangalore,Nov,

32 Preliminary analysis: System 2 at z = 1.37 Typeset by FoilTEX IAS, Bangalore,Nov,

33 Preliminary analysis: System 2 PLot file version 1 created 07-AUG :22:58 CONT: J IPOL MHZ J ICL Center at RA DEC Cont peak flux = E-01 JY/BEAM Levs = 5.000E-03 * (-1, 1, 2, 4, 8, 16, 32, 64, 128, 256, 512) 8.3 MHz 2.3 MHz 1.4 MHz Typeset by FoilTEX IAS, Bangalore,Nov,

34 Using 21-cm absorption lines: Typeset by FoilTEX IAS, Bangalore,Nov,