Our paper “ALMA High-Level Data Products: Submillimetre counterparts of SDSS quasars in the ALMA footprint” is accepted for publication in the Monthly Notices of the Royal Astronomical Society. This paper presents the first instance of the High-Level Data Products initiative run at the European ALMA Regional Centre, a catalogue of SDSS quasars observed with ALMA observatory. Here’s a short overview of the paper.
Motivation
Re-usage statistics of ALMA projects.
The Atacama Large Millimeter/ submillimeter Array (ALMA) has been observing the skies for 10 years, and in that time, it has generated a vast archive that is used extensively. ALMA currently generates about 300-400 TB of raw and reduced data per year. ALMA data are used over and over again to produce original science. And yet, there are thousands of observation which remain unpublished. Due to over-subscription, getting new PI observations is hard, while the potential of archival research is growing.
In response to this, the European ALMA Regional Center (EU-ARC) network launched the High-Level Data Products (HLDP) initiative. Its goal is to develop science-oriented data products derived from data sets publicly available in the ALMA Science Archive (ASA), that go beyond the formal ALMA deliverables. The result of this first instance of HLDP is the creation of a catalogue of submillimeter counterparts of the SDSS Quasars.
When creating the SED of quasars, the submillimeter is an oft-neglected part of the spectrum. Our current knowledge on the far-infrared (FIR) to millimeter properties of quasars is based on observations with poor spatial resolution (e.g. with Herschel), making it difficult to identify counterparts at other wavelengths. SEDs of quasars at wavelengths beyond a few tens of micron are often poorly defined, consequently affecting properties derived from those SEDs, such as SFRs in quasar hosts, dust temperatures etc. This catalogue is a first step towards a study of submillimeter properties of quasars in greater detail.
Catalogue
An example of an ALMA detection of a SDSS quasar. The black square shows the position of the ALMA detection and the red circle shows the coordinates of the SDSS quasar.
We present 376 submillimeter detections of SDSS DR14 quasars, corresponding to 275 unique quasars, in the ALMA footprint. 87% were targeting the SDSS quasar (i.e. the observations are centred on the quasar), while for the remaining cases the quasar just happened to be on an ALMA image centred on a different target. 70% of the objects are in the redshift range between 1 and 3, encompassing the peak of quasar activity, and bolometric luminosity of 10^45 - 10^48 erg/s.
ALMA counterparts were detected in observations carried out in bands 3 to 9, with most observations being done in bands 3, 4, 6, and 7. The bright fluxes in bands 3 and 4 (above a couple tens of mJy) are indicative of synchrotron emission out to redshifts of ~2, while the bulk of bands 6 and 7 emission (at redhifts above ~1.3) traces star formation in the hosts of the quasars. The ALMA observations cover, depending on redshift and band, the rest frame wavelengths between ~190 micron and ~1.8 mm for the majority of the sample. The main contributor to the emission at these wavelengths is dust, heated by star formation processes in the quasar hosts, with some contribution from the circumnuclear dust heated by the AGN. Non-thermal (synchrotron) emission from the nucleus, at least in the case of radio-loud quasars, may pitch in to the mm wavelengths, however with single measurements per object it is not possible to distinguish between the thermal and non-thermal components. Nevertheless, the flux measurements provided in the catalogue are relevant to a number of AGN-related studies.
The first 20 lines in the main catalogue of DR14Q quasars with ALMA detections.
The catalogue is available online on MNRAS webpage. We also provide a list of DR14 quasars within the ALMA footprint, for which no detection above an SNR cut of 3.5 was found. We also briefly discuss some interesting and unique sources detected during visual inspection, including jetted quasars, lensed quasars, and quasars with close companions. These would be of interest to the community.
SDSS quasars with ALMA counterparts and a secondary ALMA companion (physical or in projection).
With its high spatial resolution, ALMA observations of FIR-bright quasars help identify the source of the far infrared/submillimeter emission and provide an accurate estimate of the fluxes. This is particularly important for creating the SEDs of quasars, which can affect the accuracy of derived properties such as star formation rates and dust temperatures.
This catalogue is an important resource for studying quasars and active galactic nuclei. Upcoming instances of ALMA HLDP and HLDP-like initiatives will cater to a large variety of science cases. The potential for the creation of value-added, science-ready data products is large and is increasing as more data are added to the ASA every day, providing new possibilities for original, ground-breaking research.
The paper is available to read on the MNRAS website or the preprint on arXiv.