[Paper Review] The AKARI FIS YSO Catalogue

L. Viktor Tóth, G. Marton+7 more|arXiv (Cornell University)|Sep 24, 2013

Astrophysics and Star Formation Studies60 references18 citations

TL;DR

This paper presents the AKARI FIS YSO Catalogue, a new all-sky catalogue of 44,001 young stellar object (YSO) candidates derived from AKARI Far-Infrared Surveyor and WISE photometric data using Quadratic Discriminant Analysis (QDA) classification. The method achieves over 90% reliability in identifying YSOs, with 76% of candidates being previously uncatalogued, predominantly Class I and II sources, and shows strong spatial correlations with galactic ISM structures including infrared loops and Planck cold clumps.

ABSTRACT

We demonstrate the use of the AKARI survey photometric data in the study of galactic star formation. Our aim was to select young stellar objects (YSOs) in the AKARI FIS catalogue. We used AKARI Far-Infrared Surveyor and Wide-field Infrared Survey Explorer data to derive mid- and far-infrared colours of YSOs. Classification schemes based on Quadratic Discriminant Analysis have been given for YSOs. The training catalogue for QDA was the whole sky selection of previously known YSOs (i.e. listed in SIMBAD). A new catalogue of AKARI FIS YSO candidates including 44001 sources has been prepared. Reliability of the classification is over 90% as tested in comparison to known YSOs. As much as 76% of our YSO candidates are from previously uncatalogued type. The vast majority of these sources are Class I and II types according to the Lada classification. The distribution of AKARI FIS YSOs' is well correlated with that of the galactic ISM. Local over densities were found on infrared loops and towards the cold clumps detected by Planck.

Motivation & Objective

• To identify and classify young stellar objects (YSOs) in the all-sky AKARI FIS Bright Source Catalogue using multi-wavelength infrared photometry.
• To develop a robust classification scheme based on mid- and far-infrared colours to distinguish YSOs from other stellar and interstellar sources.
• To investigate the large-scale spatial distribution of YSO candidates in relation to galactic interstellar medium (ISM) structures such as infrared loops and Planck cold clumps.
• To assess the reliability and completeness of the YSO catalogue by comparing with known YSOs in SIMBAD and using statistical validation methods.
• To explore the physical conditions and critical thresholds for star formation by analyzing correlations between YSO surface density and ISM properties.

Proposed method

• Utilized AKARI FIS all-sky photometric data in four bands (65, 90, 140, 160 µm) and WISE data in mid-infrared bands (3.4, 4.6, 12, 22 µm) to derive multi-band infrared colours for source classification.
• Applied Quadratic Discriminant Analysis (QDA) to classify sources into YSO classes using a training catalogue of known YSOs from SIMBAD.
• Calibrated the classification reliability by cross-matching with known YSOs, achieving a 90%+ accuracy rate in identifying true YSOs.
• Mapped the spatial distribution of YSO candidates and compared it with galactic CO emission (Dame et al. 2001), infrared loops (GIRLs), and Planck Early Cold Clumps (ECCs).
• Performed Monte Carlo simulations to test the statistical significance of observed overdensities of YSOs around loops and clumps.
• Defined a critical column density threshold (1.6×10²² cm⁻²) for star formation based on correlation with Planck ECC clumps and CO column density analysis.

Experimental results

Research questions

• RQ1 What is the reliability and completeness of YSO classification in the AKARI FIS BSC using multi-wavelength infrared colours?
• RQ2 How do the spatial distributions of AKARI YSO candidates correlate with galactic ISM structures such as infrared loops and Planck cold clumps?
• RQ3 What is the critical column density of molecular gas above which star formation is significantly triggered?
• RQ4 Are YSOs preferentially associated with specific ISM features like infrared loops or cold clumps, and is this association statistically significant?
• RQ5 How do the physical properties of Planck ECC clumps differ between those with and without associated YSOs?

Key findings

• The AKARI FIS YSO Catalogue contains 44,001 YSO candidates, with 76% being previously uncatalogued sources.
• The classification reliability exceeds 90% when validated against known YSOs from SIMBAD.
• The majority of YSO candidates (over 90%) are classified as Class I or Class II according to the Lada classification scheme.
• A significant overdensity of YSOs is found on 98 infrared loops (GIRLs), with 43 showing a statistically significant excess in star formation, particularly in the outer Galaxy.
• Among Planck ECC clumps, 41.4% contain at least one associated YSO within twice the clump's major axis, and all clumps with associated YSOs have temperatures above 6.7 K.
• A critical column density threshold of 1.6×10²² cm⁻² for star formation is identified, above which all clumps are found to host YSOs within their double-major-axis radius.