Multi-wavelength surveys
Large-area, multi-wavelength surveys are some of the best tools we have to probe both the local and the early Universe and attack long-standing questions in astronomy with statistical vigour. Given their relative rarity (~10% of all galaxies), large-area surveys can help us identify large samples of AGN. The fact that AGN emit over the full electromagnetic spectrum facilitates this search, in the sense that we can use a wide array of instruments, as well as selection techniques, to pick out AGN. At the same time however, most AGN observational signatures are not unique to AGN but rather can originate in diverse astrophysical environments. AGN survey astronomy deals with identifying AGN, while accounting for the contamination from non-active galaxies and intra-galactic objects, decomposing their emission from the emission of their hosts, and constraining their intrinsic properties (like their bolometric luminosity, their black hole mass, etc.).
Surveys in the radio wavelengths
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Radio surveys detect emission from both active galaxies, synchrotron emission from their radio jets, as well as star forming galaxies, both thermal and non-thermal emission from supernovae shocks. Current and next-generation radio telescopes like LOFAR and SKA will revolutionize the way we observe galaxies and will bring radio astronomy to the forefront of survey astronomy.
I am a member of the Australia Telescope Large Area Survey (ATLAS) and Evolutionary Map of the Universe (EMU) large-area surveys in the radio wavelengths, led by Prof. Ray Norris at McQuarie University, Sydney, Australia. ATLAS used the Australian Telescope Compact Array (ATCA) to image a large part of the Southern sky (~10 sq. degree) at several radio frequencies. EMU will use the Australian Square Kilometre Array Pathfinder (ASKAP) to image 3000 times the area covered from ATLAS to much deeper sensitivities and better resolution.
I have also worked with the Caltech-Jodrell Bank Flat-Spectrum (CJF) sample, which was created through the combination of several radio interferometric campaigns at 5 GHz.
Mid-infrared surveys
Mid-infrared surveys are extremely potent as they can penetrate obscuration from dust, while retaining good sensitivity and relatively good resolution. They are however limited by Earth's atmosphere, which absorbs most mid-infrared emission. As a result, mid-IR surveys have been mostly carried out by space telescopes. Both AGN and star formation emission, absorbed and re-emitted by dust can be seen at mid-infrared wavelengths. The decomposition of the two is an active field of research.
I am a member of the AKARI North Ecliptic Pole (NEP) field survey. AKARI was a Japanese-led space observatory that observed the sky from near- to far-infrared wavelengths. The key advantage of AKARI was its unprecedented contiguous wavelength coverage at mid-infrared wavelengths. This allowed a detailed decomposition of the emission into star formation and AGN origins.
The NEP field is one of the premier deep survey fields on the sky due to both its coverage by AKARI but and by a slew of other ground-based and space-born telescopes in wavelengths that range from the radio to the X-rays.
Related papers: Karouzos et al. 2012, Karouzos et al. 2014, Goto et al. 2015
Near-infrared surveys
Near-infrared surveys offer distrinct advantages over mid-infrared surveys, both in the better resolution and sensitivity achievable from the ground, while still offering more penetration power than traditional optical surveys. Infrared data can also help us to look at rest-frame optical and UV emission from high redshift galaxies and is hence indespensable for identifying AGN in the early Universe.
I am member of the VISTA Deep Extragalactic Observations (VIDEO) survey, a large ESO VISTA program led my Prof. Matt Jarvis at the university of Oxford. VIDEO covers several of the most famous survey fields on the sky in near-infrared filters reaching up to a few micron wavelengths.
I am also member of the Infrared Medium-Deep Survey (IMS), a large program led by Prof. Myungshin Im using UKIRT and other smaller telescopes to map a large area of the sky at near-infrared wavelengths. The primary goal of the survey is the identification of very high redshift quasars, but the applications of this dataset are numerous and diverse.
Related papers: Karouzos et al. 2014a, Karouzos et al. 2014c, Kim et al. 2015, Jarvis et al. 2013
Optical surveys
Optical surveys offer the best sensitivity, in terms of the instruments available for both ground-based and space-born observations. Together with their relative insensitivity to atmospheric conditions and the development of adaptive optics techniques, optical observations make for some of the best datasets in our disposal to study local and intermediate redshift objects in great detail. However, optical emission is susceptible to dust, with highly extinct objects being completely opaque at optical wavelengths.
As part of the AKARI NEP follow-up, I have participated in a number of optical photometric and spectroscopic surveys. The latter in addition offer information about the physical processes powering the observed sources (photoionization, metallicities, star formation rates, etc.). The former include large optical surveys using the CFHT and the Suprime-Cam on the Subaru telescope. Optical observations can be crucial to constrain the redshift of sources at intermediate redshifts, where spectoscopic data become exceedinly hard to acquire.
Related papers: Shim et al. 2013