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Detection of H-alpha emission from z>3.5 galaxies withAKARI-FUHYU NIR spectroscopy Chris Sedgwick Stephen Serjeant Chris Pearson The Open University on behalf of the FUHYU mission program
Phase III FUHYU Mission Program • The FUHYU mission program (PI Chris Pearson) • Phase I & II: extensive infrared imaging of well-studied fields • Serjeant et al 2009, Negrello et al 2009, Pearson et al 2010 • Phase III (warm phase): spectroscopy of well-studied sources • In total, 552 spectroscopic pointingsacross 72 sources • For galaxies discussed today, the science objective was to measure rest-frame optical emission lines of star-forming galaxies at very high redshifts 速い 安い 上手い
Observations • IRC NIR instrument (others turned off in warm phase) • N3 imaging filter at 3 microns. Imaging field of view about 10’x10’ (412x512 pixels) with pixel scale of 1.46” and PSF 3.2 pixels • Target guided into the 1’x1’ aperture Np dedicated to spectroscopy • NG grism with wavelength range 2.5 - 5.0 microns across 291 pixels with a dispersion of 0.0097 microns per pixel • AOT IRCZ4 contains 5 initial dark frames, 4 exposure frames for NG, then an N3 reference image, then 4 or more additional NG frames and finally 5 more dark frames • 10 pointings per target wherever possible, each of about 10 minutes
Data Reduction • IRC data reduction pipeline was adapted for the warm phase (Onaka et al 2009) and originally used to reduce our data • However we found it necessary to make bespoke corrections for spacecraft jitter between sub-frames and sky subtraction and de-glitching • We also used routines previously developed for SCUBA for zero-footprint drizzling and noise-weighted feature extraction (Serjeant et al. 2008) • Developed an IDL GUI routine to visualise various elements of the reduction on an interactive basis, and the pointings were optimally combined with noise-weighted co-adding
High-redshift Radio and Submillimetre Galaxies We targeted four high-redshift radio galaxies (redshifts known from Ly-alpha lines), and three submillimetre galaxies believed to be associated with one of them.
8C1909+722 and its 3 companion submillimetre galaxies HzRG SMM1 SMM2 SMM3 SMM1 and SMM2 are roughly aligned with the jet from the radio galaxy (Stevens et al. 2003)
8C1909+722 HzRG Halpha
8C1909+722 SMM1a Halpha
8C1909+722 SMM1b Halpha
8C1909+722 SMM2 Halpha
8C1909+722 SMM3 Halpha
Summary of 8C1909+722 HzRG and companion galaxies HzRG – good Halpha line SMM1a – no convincing detection SMM1b – strong Halpha, slightly displaced SMM2 – good Halpha line SMM3 – no convincing detection
The other 3 high-redshift radio galaxies 8C1435+635 Z = 4.261 4C60.07 Z = 3.788 4C41.17 Z = 3.792
Spectra for other three radio galaxies observed 8C1435_635 (z=4.261)No convincing H-alpha detection 4C60.07 (z=3.788)Broad peak just above expected H-alpha (probable identification) 4C41.17 (z=3.792)No convincing H-alpha detection
A closer look at 4C 60.07 (z=3.788) H-alpha peak is displaced from the expected wavelength, possibly because the dispersion axis is aligned with a companion submillimetre galaxy Spitzer average 3.6 and 4.5 micron images with superimposed SMA 890 micron image and contours. Square is radio galaxy; A and B are submillimetre components. Image from Ivison et al (2008).
Star formation rates and evidence of quasars • Star Formation Rates (SFRs) estimated from the H-alpha lines of these galaxies (using Kennicutt 1998) is a factor of ~20 lower than the SFRs estimated from far infrared luminosity, suggesting strong dust obscuration • Three of these sources are HyLIRGs (L > 1013Lsolar) • The FWHM of the H-alpha line for each of these galaxies is high, particularly for the two radio galaxies, suggesting that dust-shrouded quasars are present
Summary • H-alpha emission detected for four galaxies at redshifts 3.5 – 3.8 • Two submillimetre galaxies are at the same redshift as companion high-redshift radio galaxy, confirming the conclusion by Stevens et al (2003) that they are part of the same extensive star-forming cluster • Star formation rates estimated from H-alpha lines show a decrement by a factor of ~20 from FIR-estimated SFRs suggesting strong dust obscuration in the galaxies • The FWHM of the H-alpha lines show strong evidence of dust-shrouded quasar activity in both the radio galaxies
Extra slide Example of comparison between IRC and OU pipelines (1370153.9) Top: raw spectrum output from IRC pipeline Middle: IRC pipeline with extra sky subtraction and Gaussian across several (spatial) columns Bottom: OU pipeline
Extra slide • Comparison of H-alpha line luminosity with other ULIRGS • ( still work in progress)