# Analysis and test of the central-blue-spot infall hallmark

## TL;DR

This paper investigates the central-blue-spot infall hallmark in star-forming regions, deriving analytical models, accounting for observational resolution effects, and applying the method to real data to confirm its reliability as an infall indicator.

## Contribution

It provides an analytical framework for the central-blue-spot infall hallmark, including effects of finite resolution, and validates it with observational data from multiple star-forming regions.

## Key findings

- Good fits to observed moment maps were achieved.
- Estimated central masses range from 0.1 to 120 solar masses.
- The hallmark is confirmed as a robust infall indicator.

## Abstract

The infall of material onto a protostar, in the case of optically thick line emission, produces an asymmetry in the blue- and red-wing line emission. For an angularly resolved emission, this translates in a blue central spot in the first-order moment (intensity weighted velocity) map. An analytical expression for the first-order moment intensity as a function of the projected distance was derived, for the cases of infinite and finite infall radius. The effect of a finite angular resolution, which requires the numerical convolution with the beam, was also studied. This method was applied to existing data of several star-forming regions, namely G31.41+0.31 HMC, B335, and LDN 1287, obtaining good fits to the first-order moment intensity maps, and deriving values of the central masses onto which the infall is taking place (G31.41+0.31 HMC: 70-120 $M_\odot$; B335: 0.1 $M_\odot$; Guitar Core of LDN 1287: 4.8 $M_\odot$). The central-blue-spot infall hallmark appears to be a robust and reliable indicator of infall.