An ALMA survey of the SCUBA-2 Cosmology Legacy Survey UKIDSS/UDS field: Identifying candidate z~4.5 [CII] emitters
Summary (2 min read)
- High-redshift (z3) SMGs therefore appear to play a potentially significant role in galaxy evolution; however, their dusty nature and high redshift mean that measuring their spectroscopic redshifts—needed to constrain many of their basic properties—is extremely challenging using ground-based optical/near-infrared spectroscopy.
- [C II] emission can originate both in photodissociation regions around star-forming regions and also from atomic and ionized gas (e.g., Dalgarno & McCray 1972; Madden et al. 1997; Pineda et al. 2013). [C II] could thus provide information about the volume and extent of the cold gas reservoir and star formation in galaxies.
2.1. ALMA Data
- These cubes were first continuum-subtracted by subtracting a linear fit to the continuum in the spectrum of each pixel.
- In one of these SMGs (AS2UDS.0109.1) the authors found a tentative S/N=5.3 emission line corresponding to the same redshift as the detected emission line source (AS2UDS.0109.0).
- 18 In each collapsed 100 km s−1 slice the authors search in the narrowband image for peaks above 2σ within the ALMA primary beam.
2.2. Multi-wavelength Data
- The UDS has photometric coverage spanning the optical, near-, mid-, and far-infrared, out to radio wavelengths.
- This figure also shows a zoomed-in 3″×3″optical/infrared image of each source, with the ALMA continuum contours overlaid.
- The deblending uses a combination of the ALMA-detected SMGs and Spitzer/MIPS 24 μm and UDS20 radio sources as positional priors for the deblending of the low-resolution SPIRE maps.
3. Results and Discussion
- The authors provide the source redshifts and line properties in Table 1.
- The line flux densities are calculated from the Gaussian profile fit to each line.
- The deblended catalogs for the fields are available from http://astro.dur.ac.
- The number of line emitters the authors identify from the parent sample of 695 SMGs is consistent with the expectation from the ALESS survey, where two emission line sources were identified from a sample of 99 SMGs (Swinbank et al. 2012).
3.1. Alternative Emission Lines
- Before the authors discuss the properties of their line-emitter galaxies, they first discuss the identification of the emission lines.
- 2. [C II] Luminosities and Line Widths Figure 3 shows the FWHM and emission line luminosities of their 10 sources (with those that are potentially lower-redshift or lensed flagged) compared to other studies of high-redshift starforming galaxies and AGNs.
- To investigate the “[C II] deficit” the authors must first estimate the infrared (rest-frame 8–1000 μm) luminosities of their line emitters.
3.5. z∼4.5 SMGs are Warm
- Comparing their inferred dust temperatures and far-infrared luminosities in Figure 7, their sample of z∼4.5 SMGs appears to have warmer characteristic dust temperatures at fixed luminosity than inferred for z;2 SMGs and star-forming galaxies (e.g., Magnelli et al.
- In this section the authors first test the reliability of their measured dust temperatures and then discuss the implications of warm dust temperatures on the selection of high-redshift SMGs.
- Figure 8 shows the [C II] luminosity function at z∼4.5 as derived from their sample of seven S870>4 mJy continuum-selected [C II] emitters.
- The authors observations at the bright end of the luminosity function suggest that the model of Lagache et al. (2018) overpredicts the [C II] luminosity function at this redshift unless their sample selection is incomplete, which is possible.
- All of these line emitters are 870 μm continuum-detected sources in their parent survey with S8701 mJy.
- The extended [C II] emission compared to the dust continuum together with the measured infrared luminosities in these SMGs combines to give a star formation rate surface density measurement of 130±20 M yr −1 kpc−2.
- I.R.S. also acknowledges support from a Royal Society/Wolfson Merit Award.
- The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ.
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Q1. What have the authors contributed in "An alma survey of the scuba-2 cosmology legacy survey ukidss/uds field: identifying candidate z ∼ 4.5 [c ii] emitters" ?
The authors report the results of a search for serendipitous [ C II ] 157. 74 μm emitters at z ; 4. 4–4. 7 using the Atacama Large Millimeter/submillimeter Array ( ALMA ). From stacking the high-resolution ( ∼0 15full-width half maximum ) ALMA 870 μm imaging, the authors show that the [ C II ] line emission is more extended than the continuum dust emission, with an average effective radius for the [ C II ] of r 1. 7 e 0. 2 0. 1 = + kpc, compared to re=1. 0±0. 1 kpc for the continuum ( rest-frame 160 μm ). By fitting the far-infrared photometry for these galaxies from 100 to 870 μm, the authors show that SMGs at z∼4. The authors discuss the implications of this result in terms of the selection biases of high-redshift starbursts in far-infrared/submillimeter surveys. The authors detect 10 candidate line emitters, with an expected false detection rate of 10 %. 5 10 Mpc 6 3 > ́ on the space density of luminous ( LIR ; 10 13 L ) SMGs at z=4. 40–4. 66, suggesting 7 % of SMGs with S 1 870 m m mJy lie at 4 < z < 5.