DESHIMA on ASTE: Sky removal method for astronomical observations with an ultra-wideband submillimeter spectrometer

25 Jul 2019, 17:45
1h 15m
Piazza Città di Lombardia (Milano)

Piazza Città di Lombardia

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI
Poster Detector readout, signal processing, and related technologies Poster session

Speaker

Dr Akio Taniguchi (Nagoya University)

Description

We are developing an ultra-wideband spectroscopic instrument, DESHIMA, a spectrometer integrated on-chip filterbank and microwave kinetic inductance detector (MKID) technologies to investigate dusty starburst galaxies in the distant universe at millimeter and submillimeter wavelength. On-site experiment of prototype DESHIMA was promoted using the ASTE 10-m telescope in Oct. and Nov. 2017. In this session, we used 49 frequency pixels in 332-377 GHz band (frequency step of $\sim$1 GHz), and successfully detected some astronomical molecular lines such as the redshifted CO (J=3-2) line of VV 114, a luminous infrared galaxy at $z$=0.020.

In this poster, we present a method to remove a spectrum of sky emission from an observed time-series data of DESHIMA. Because of ultra-wideband ($\sim$45 GHz in prototype, $>$200 GHz in full operation), the time variation of atmospheric opacity, $\tau(t)$, is no longer constant over the waveband but has a frequency dependency, $\tau(\nu,t)$. This makes a spectral sky baseline strongly non-linear, which may fail the conventional sky removal using a constant or polynomial baseline estimates. With the ALMA atmospheric model, we calculate the frequency-dependent $\tau(\nu,t)$ as a function of frequency-independent precipitable water vapor, PWV$(t)$. We then fit the sky baseline of each time-series spectrum by estimating PWV$(t)$ and constant value, $C(t)$, instead of coefficients of a polynomial function. We demonstrate that the proposed method mitigates the non-flatness of an estimated astronomical spectrum compared to the conventional one in several DESHIMA data. We also find that the method enables us to keep continuum emission as $C(t)$, which may offer a new way of sky removal for continuum observations where we cannot adopt conventional method.

Student (Ph.D., M.Sc. or B.Sc.) N
Less than 5 years of experience since completion of Ph.D Y

Primary author

Dr Akio Taniguchi (Nagoya University)

Co-authors

Dr Yoichi Tamura (Nagoya University) Dr Tom Bakx (Nagoya University) Mr Koyo Suzuki (Nagoya University) Tatsuya Takekoshi (The University of Tokyo) Prof. Kotaro Kohno (The University of Tokyo) Dr Takashi Tsukagoshi (National Astronomical Observatory of Japan, Mitaka) Dr Tai Oshima (National Astronomical Observatory of Japan) Akira Endo (Delft University of Technology) Dr Soh Ikarashi (TU Delft) Kenichi Karatsu (TU Delft)

Presentation Materials