Research

I am interested in the problem of understanding the nature of BAL QSOs. The optical spectra of these objects show wide absorptions bluewards the prominent UV resonance lines. These absorbing troughs trace gas outflows with velocities as high as 0.2c. Why only a fraction of all QSOs show BALs and what are the physical conditions of these outflows are still unknown questions.

The two main scenarios trying to explain the origin of the BAL phenomenon are:

• Orientation scenario:
  Only the fraction of QSOs seen from a certain viewing angle show BALs. The winds are non isotropic and therefore cannot be detected from all directions.
• Evolutionary scenario:
  BAL winds develop in most quasars during specific periods in their lifetime, perhaps while expelling their dusty cocoons and evolving into normal QSOs.

My research has focused on the characterisation of the radio properties of radio-loud BAL QSOs in order to obtain orientation indicators (radio spectral indices, milliarcsecond morphology) and hints about their evolutionary status (spectral aging). The amount of dust is also a property that should be different in both proposed scenarios.

In Montenegro-Montes et al. (2008; MNRAS 388, 1853) we found that radio sources associated with BAL QSOs recall a well known type of radio sources: Compact Steep Spectrum (CSS) and Gigahertz-Peaked sources (GPS). These are young radio sources which show compact morphology as well as steep and peaked radio spectra. An estimate of the age of these sources can be done through a spectral aging analysis (Murgia et al. 1999; A&A 345, 769).

Polarisation constitutes also a powerful diagnostic tool to probe the physical conditions of CSS and GPS radio sources. In particular, through the determination of the depolarisation index and Rotation Measures. (e.g. Mantovani et al. 2009; A&A, 502, 61)