Infrared spectroscopy of intermediate mass young stellar objects

TL;DR

This study uses Spitzer infrared spectroscopy to analyze 14 intermediate-mass young stellar objects, revealing their physical properties, environmental features, and excitation mechanisms through spectral analysis and imaging correlations.

Contribution

It provides a detailed spectral classification and physical characterization of intermediate-mass YSOs, including environmental diagnostics and excitation mechanisms, using Spitzer data.

Findings

Identification of two object types based on spectral features

Detection of atomic fine structure lines like [NeII]

Correlation of spectral features with spatial morphologies

Abstract

In this paper we present Spitzer Infrared Spectrograph spectroscopy for 14 intermediate-mass young stellar objects. We use Spitzer spectroscopy to investigate the physical properties of these sources and their environments. Our sample can be divided into two types of objects: young isolated, embedded objects with spectra that are dominated by ice and silicate absorption bands, and more evolved objects that are dominated by extended emission from polycyclic aromatic hydrocarbons (PAHs) and pure H2 rotational lines. We are able to constrain the illuminating FUV fields by classifying the PAH bands below 9micron. For most of the sources we are able to detect several atomic fine structure lines. In particular, the [NeII] line appearing in two regions could originate from unresolved photodissociation regions (PDRs) or J-shocks. We relate the identified spectral features to observations obtained from NIR through submillimeter imaging. The spatial extent of several H2 and PAH bands is matched with morphologies identified in previous Spitzer/IRAC observations. This also allows us to distinguish between the different H2 excitation mechanisms. In addition, we calculate the optical extinction from the silicate bands and use this to constrain the spectral energy distribution fit, allowing us to estimate the masses of these YSOs.