Source identification number.

Redshift quality flag, ranging from 1 for very insecure redshifts to 4 corresponding to secure redshifts.

Instrument used to select the source;

galaxy classification: according to the optical spectral features, objects have been classified into ELGs and ALGs.

Classification based on X-ray emission (see Sect. 6.3).

Classification based on emission line optical spectra, using diagnostic diagrams (BPT; Baldwin et al. 1981; Veilleux & Osterbrock 1987, see Fig. 12);

region where the source lands (A, B, C in Fig. 1, the symbol * indicates the red elliptical region in Fig. 1, which has been excluded by the X-ray analysis);

distance from the cluster centre in arcmin;

log(2–10 keV unabsorbed luminosity). At the Bullet’s redshift the flux limits the A, B, and C regions correspond to a 2–10 keV luminosity of ∼1.5 × 10⁴¹ erg s⁻¹, ∼2 × 10⁴¹ erg s⁻¹, ∼3.5 × 10⁴¹ erg s⁻¹, respectively.

N_H in unit of 10²² cm⁻², evaluated by the (H−S)/(H+S) ratio using an absorbed power-law spectrum with Γ = 1.9;

X/O ratio: the optical flux is computed by converting R magnitudes in specific fluxes and then multiplying by the width of the Rc filter (f_R(0) = 2.15 × 10⁻⁹ erg cm⁻² s⁻¹ Å⁻¹, Δλ_R = 1568 Å, Fukugita et al. 1995).

SFR in M_⊙ yr⁻¹, evaluated by the 2–10 keV luminosity using the relation from Ranalli et al. (2003);

SFR in M_⊙ yr⁻¹, evaluated by the Hα luminosity using the relation from (Kennicutt et al. 1994);

redshift from a literature (see text);

the X-ray spectrum of the source #13 (see Sect. 4.4, Fig. 5 and Table 3) shows a strong iron emission, which suggests a column density larger than 10²⁴ cm⁻².