Arimax and Auto.arima for Multi variate time series forecasting

Hi All,

I'm trying to do a Multivariate time series forecasting. The data set contains one dependent and independent variable.
From the cross-co relation the 0 day lag of the independent variable seems to have better correlation with dependent variable.

But I need some clarification on which function should use auto.arima() with xreg or arimax()

  1. While using auto.arima() to predict the dependent variable by using independent Variable on the xreg parameter,Do we need to have xreg values in place already for the forecast periods?
  2. Or can we use arimax() to predict the dependent variable along with a covariate even if there are no values available for the covariate on the forecast period

Please advise

Thank you