Optical Extinctions of Inter-Arm Molecular Clouds in M31: A Pilot Study for the Upcoming CSST Observations

TL;DR

This study proposes using optical extinction measurements from space telescopes, particularly the upcoming CSST, to identify inter-arm molecular clouds in M31, offering an alternative to sub-millimeter emission techniques limited by sensitivity.

Contribution

It introduces a novel optical extinction method utilizing CSST data for detecting inter-arm molecular clouds, validated with existing data and mock catalogs, enhancing distant galaxy studies.

Findings

Optical extinction AV > 1.6 mag indicates inter-arm molecular clouds.

Most clouds show AV around 1 mag, consistent with JCMT data.

CSST mock data effectively identifies clouds with AV > 1.6 mag.

Abstract

Recent sub-millimeter dust thermal emission observations have unveiled a significant number of inter-arm massive molecular clouds in M31.However,the effectiveness of this technique is limited to its sensitivity,making it challenging to study more distant galaxies.This study introduces an alternative approach,utilizing optical extinctions derived from space-based telescopes,with a focus on the forthcoming China Space Station Telescope(CSST).We first demonstrate the capability of this method by constructing dust extinction maps for 17 inter-arm massive molecular clouds in M31 using the Panchromatic Hubble Andromeda Treasury(PHAT) data.Our analysis reveals that inter-arm massive molecular clouds with an optical extinction(AV) greater than 1.6 mag exhibit a notable AV excess,facilitating their identification.The majority of these inter-arm massive molecular clouds show an AV around 1 mag,aligning with measurements from our JCMT data.Further validation using a mock CSST RGB star catalog confirms the method's effectiveness.We show that the derived AV values using CSST z and y photometries align more closely with the input values.Molecular clouds with AV>1.6 mag can also be identified using the CSST mock data.We thus claim that future CSST observation could provide an effective way for the detection of inter-arm massive molecular clouds with significant optical extinction in nearby galaxies.