HH 24A2 , the SIMBAD biblio

We present an in-depth near-IR analysis of a sample of H₂ outflows from young embedded sources to compare the physical properties and cooling mechanisms of the different flows. The sample comprises 23 outflows driven by Class 0 and I sources having low-intermediate luminosity. We have obtained narrow band images in H₂ 2.12µm and [FeII] 1.64µm and spectroscopic observations in the range 1-2.5µm. From [FeII] images we detected spots of ionized gas in ∼74% of the outflows which in some cases indicate the presence of embedded HH-like objects. H₂ line ratios have been used to estimate the visual extinction and average temperature of the molecular gas. A_v values range from ∼2 to ∼15mag; average temperatures range between ∼2000 and ∼4000K. In several knots, however, a stratification of temperatures is found with maximum values up to 5000K. Such a stratification is more commonly observed in those knots which also show [FeII] emission, while a thermalized gas at a single temperature is generally found in knots emitting only in molecular lines. Combining narrow band imaging (H₂, 2.12µm and [FeII], 1.64µm) with the parameters derived from the spectroscopic analysis, we are able to measure the total luminosity of the H₂ and [FeII] shocked regions (L_H2 and L_[FeII]) in each flow. H₂ is the major NIR coolant with an average L_H2/L_[FeII] ratio of ∼10². We find that ∼83% of the sources have a L_H2/L_bol ratio ∼0.04, irrespective of the Class of the driving source, while a smaller group of sources (mostly Class I) have L_H2/L_bol an order of magnitude smaller. Such a separation reveals the non-homogeneous behaviour of Class I, where sources with very different outflow activity can be found. This is consistent with other studies showing that among Class I one can find objects with different accretion properties, and it demonstrates that the H₂ power in the jet can be a powerful tool to identify the most active sources among the objects of this class.