Detection of H-alpha emission from z>3.5 galaxies with

AKARI-FUHYU NIR spectroscopy

Chris SedgwickStephen SerjeantChris Pearson

The Open Universityon 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 2010Phase III (warm phase): spectroscopy of well-studied sourcesIn total, 552 spectroscopic pointings across 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

ObservationsIRC 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

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

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)

Larger view of pipeline Graphic User Interface

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.

Object RA (h m s) Dec (d m s) Redshift Flux 850um/mJy

No. of Pointings

8C1909+722 HzRG 19 08 23.3 +72 20 10.4 3.536 34.9 10

8C1909+722 SMM1 19 08 27.4 +72 19 28.0 23.0 10

8C1909+722 SMM2 19 08 29.3 +72 20 49.6 8.7 10

8C1909+722 SMM3 19 08 16.1 +72 20 24.0 4.3 13

8C1435+635 HzRG 14 36 37.4 +63 19 13.1 4.261 6.0 10

4C60.07 HzRG 05 12 54.8 +60 30 51.7 3.788 23.8 10

4C41.17 HzRG 06 50 52.1 +41 30 30.8 3.792 12.0 7

8C1909+722 and its 3 companion submillimetre galaxies

SMM1 and SMM2 are roughly aligned with the jet from the radio galaxy (Stevens et al. 2003)

HzRG SMM1 SMM2 SMM3

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

SMM1b – strong Halpha, slightly displaced

SMM1a – no convincing detection

SMM2 – good Halpha line

SMM3 – no convincing detection

HzRG – good Halpha line

The other 3 high-redshift radio galaxies

8C1435+635Z = 4.261

4C60.07Z = 3.788

4C41.17Z = 3.792

8C1435_635 (z=4.261)No convincing H-alpha detection

Spectra for other three radio galaxies observed

4C41.17 (z=3.792)No convincing H-alpha detection

4C60.07 (z=3.788)Broad peak just above expected H-

alpha (probable identification)

H-alpha peak is displaced from the expected wavelength, possibly

because the dispersion axis is aligned with a companion submillimetre

galaxy

A closer look at 4C 60.07 (z=3.788)

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 (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 > 1013 Lsolar)

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

Star formation rates and evidence of quasars

Source S (Halpha) L (Halpha) SFR (Halpha) L (FIR) SFR (LFIR) FWHM (Halpha)

10-18Wm-2 1036W Msolaryr-1 1013Lsolar Msolaryr-1 km s-1

8C1909+722 HzRG 4.40 2.32 < 266 3.0 5160 9400

8C1909+722 SMM1b 3.79 2.00 81 2.0 3400 < 1700

8C1909+722 SMM2 3.30 1.74 78 0.8 1280 unresolved

4C60.07 HzRG 5.26 2.93 < 90 2.0 3490 4800

Summary

(a) H-alpha emission detected for four galaxies at redshifts 3.5 – 3.8

(b) 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

(c) 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

(d) The FWHM of the H-alpha lines show strong evidence of dust-shrouded quasar activity in both the radio galaxies

Extra slides

Example of comparison between IRC and OU

pipelines (1370153.9)

Extra slide

Top: raw spectrum output from IRC pipeline

Middle: IRC pipeline with extra sky subtraction and Gaussian across several (spatial) columns

Bottom: OU pipeline

Extra slideComparison of H-alpha line luminosity with other ULIRGS

( still work in progress)

Larger view of pipeline Graphic User Interface

HzRG 1370157

HzRG 1370162

HzRG 1370163